The hostility and negativity in this thread baffles me slightly - but then again, I am not surprised judging by the fact that we're talking about money here.
I am a small-time YouTuber myself, and I have occasionally dabbled in modding in some games in the past - and thus I can see this debate from both the aspect as a content-creator and a mod-creator. However, I am a bit curious about certain aspects of the debate here.
From a YouTuber's point of view: Factorio isn't a major game on YouTube or Twitch - it's not a massive cash-cow for a streamer or YT-video creator to make content from, like say the way Minecraft is. The audience that views videos and streams of Factorio on YT/Twitch is a very dedicated audience. If one takes a look at the channels that regularly feature Factorio on YouTube, and then have a look at the view counts for their series (not counting tutorials, which is another story altogether), you'll find that the numbers are fairly consistent - even when going back several years. Thus the actual ad/YouTube Premium revenue we're talking about for the people who use YouTube as their primary platform for producing Factorio videos is not really that high.
Then there's the aspect of Patrons - that is people who support a content creator as a whole, whether that is a YouTuber/streamer/mod-creator. I am grateful for the Patrons I have that support my own YouTube-channel, but the money I gain from my Patrons are a support to me personally and factors in all series and videos I make on my channel. So if a mod-creator wants a cut of the money I gain from making a series, I would argue that just as I have no right to intervene in said mod-creators Patron income, neither does the mod-creator have a right to intervene in any content-creators Patron income. Note that this is an argument I am making - and I am making it to see reactions from mod-creators here (please, please, please keep it civil - I am not in any way feeling entitled, I am forwarding a question - I already am highly wary of posting in this thread in the first place based on how negative I perceive some of the posts in this thread, and hostile answers will just make me back out of the thread and go back into lurking mode).
To explain why I am making the argument about Patrons: If a mod-creator has a Patreon-account, earning money from Patrons for their mod, I could make the opposite argument as the mod-creator is making (I wouldn't - this is for the sake of argument!). I.e. a content-creator could say "Hey. I am showcasing your mod on my YouTube/Twitch-channel, and thus I am going to spend a fair amount of hours into letting my audience know about your mod, which will attract attention to your mod. I would like a cut of the Patron-money you gain from the mod for spending my time and effort on showcasing your mod please."
In that argument also lies something crucial to this whole argument. Unless we're talking about some major channel - let's for the sake of argument say a YouTube channel that has hundreds of thousands of subscribers, where we assume the videos on said channel have average views of between 20 and 30 thousand per video, not counting episode 1 (to my knowledge no channel like this exists that has Factorio as one of their main featured games - but again, just for the sake of argument here) - a YouTube content-creator doesn't really make all that much money from making a series on Factorio (with or without mods).
To give people who don't do YouTube a very rough estimate: 1000 views equals about $1 of income for the YouTube channel, combined from Ad views and YouTube Premium views. Remember that any view from a non YouTube-Premium user using an AdBlocker means no income at all. Also, Google only gives estimates of how much revenue each episode have given in the analytics that a YouTube creator can see, not hard numbers, making it even harder to figure out the real numbers. And on top of that there's the persistence thing going on - the content will continue to be watched for as long as it's on YouTube, so where does an agreement of having a cut end? After 1 month, 6 months, 1 year? What about income the YouTube channel earns from the series 2 years after it was published? I have content published more than a year ago that is still watched on my channel. I hope I'm managing to convey just how complicated this is going to be for someone who does YouTube, and how it can actually drive someone who does YouTube either as a hobby or for a living away from wanting to feature a mod at all - thus I am arguing that if a mod-creator wants a cut of income, flat rates (like Patronage or similar methods) would definitely, for me, be far more relevant.
There also seems to be some misconception here about the work involved for a content-creator vs the work involved for a mod-creator. Also it is important to consider the fact that most YouTube Let's Play series have a fairly high number for episode 1, maybe episode 2-3, but the view numbers quickly starts falling by the thousands, even on the larger channels. Many people take a look at episode 1, just to hear the description of what the featured content is about, but then ignore the following episodes. A Factorio series can easily be at least 50 episodes, and I don't think I've ever seen a series have as many views on any subsequent episodes as the view count for episode 1. This phenomenon is not unique to Factorio, but applies to most game series a YouTuber who focuses on Let's Play series publish. If you research this yourself you'll find that on most channels that focuses on Let's Play series, you'll see that episode 1 in general has the highest view count, then already on episode 2 the number drops. Usually around episode 4 or 5 the number stabilises and stays fairly consistent until the last episode (the number you see there is the people who have decided to follow the series). The last episode might get a higher view count again though because some people want to see what the state of the game is at the end of the series.
To explain a little bit about the work involved in making a YouTube-series, from my own personal experience. I spend time recording the episodes, I cannot record them if I am in any negative state of mind - I must be focused, attentive, and I must also convey a sense of happiness and excitement to the viewers. Otherwise I will push any potential viewers away - people rarely want to watch content where they can sense that the presenter is miserable. So I can only record when I have energy to be a good presenter, which life doesn't always allow for. Then you have the actual time involved - which is of course the time spent per episode, usually around 30 minutes. After that there's after-processing/rendering involved. Some people, like me, have tools to automate this process - but others use tools like HitFilm Express to manually render their videos, thus increasing the time spent per episode. However, if I do a mistake, or I have to edit the video footage manually, then I have to spend time doing that as well.
But, even with automated tools involved, the computer that I do the rendering on is physically unusable while rendering, as rendering is a highly CPU/GPU consuming process. And it takes at least as long as the actual episode length (since I do not have access to insanely priced computer equipment for this) to render an episode - usually a bit longer. On top of that I also have to create a thumbnail which shows the actual episode (This is a one-time time expenditure of time per series, as per episode it only involves increasing the episode number by one and saving as a JPG), and also a description for the series and find appropriate tags for the "hidden search features" of YouTube (Also a one-time expenditure of time, but I have to pay annually for TubeBuddy to have access to automation processes here, or I would have to copy/paste for every single episode I upload).
So let's say I want to create a 50-episodes Let's Play series of Factorio - and for the sake of argument, let's say each episode is exactly 30 minutes. That's 25 hours of actual recording. Then add 2 hours to making thumbnails, writing a description and finding the correct tags. Most YouTubers who have small-to-medium channels do their own video editing, and do not use automated scripts using FFMPEG like I do, so add about 10 hours of editing to that number. And then add about 35 hours of rendering, where the computer rendering is not usable. That is a total of 72 hours - 62 hours for me with the script. So then look at my channel numbers, and I can estimate about 300 views (not counting episode 1) per episode. That is 18 600 views, and a roughly estimated total income of $18.60. I'm not going to bother doing the hourly wage calculation here.
Now, usually my impression is that mod-creators are very happy to see their mods featured on YouTube - particularly on larger channels, as it draws attention to their creations. Just as my primary goal for making videos on YouTube is to entertain people, I would also believe that a mod-creator's primary purpose is for people to play and enjoy their mods - aka entertain people. Yes, I make a small amount of money from making series. Not so much from YouTube, but that is because my channel is so small that I can barely considered dabbling in content-creation as of now - but I hope to grow my channel and in the future become larger - however, Factorio is by no means the primary game I feature on my channel personally, even though it is part of my "portfolio of games that I return to." But it's not very likely, considering the time involved and the low hourly pay, that a YouTuber would decide to showcase a mod if a mod-creator decides that they do not want to allow any monetization. Now there's absolutely nothing wrong in taking that stance as a mod-creator - but having your mod featured on a YouTube channel will substantially increase the traffic to your mod, just as having your mod featured in the FFF will.
Also, just for the sake of argument here: If Wube decides to feature a mod published under the CC-NC license in their FFF, and someone who hasn't bought Factorio decides to buy the game from them because they think that mod looks awesome, what would stop them from asking Wube for a cut from any sales made thanks to the FFF feature, since that could potentially be considered a breach of the NC part of the CC license? Note that I am not actually arguing this would be a fair thing, but it's definitely something that I'm curious about (and I am almost certain that Wube would say "No" to any such request) as it might also mean that a CC-NC licensed mod cannot be featured in the FFFs anymore without explicit written consent from the creator.
What I'm trying to say is something about the fact that there seems to be a misconception about how much money there is in making series on YouTube, or streams on Twitch, vs the hours put into the work in doing so. Mod-creators may, imho, absolutely ask for a cut if they're interested, but they should be aware that this is not a gold mine of cash. The hourly pay for doing YouTube or Twitch, unless you've got a lot of followers, is actually very low - and the smaller the channel, the less the hourly rate is. I.e. my own channel is purely for the sake of it being a hobby and something I enjoy doing. The money I gain from the people who are kind enough to support me doing YouTube stuff is about enough to allow me to buy 1 AAA title or a few indie game titles per month (Which I then usually make content on my channel with). Thus I would currently much rather just showcase another mod that doesn't require additional payment for me. Which is fine by me - but should my channel grow to a point where I actually make a decent income, I would happily support a mod-creator by becoming a Patron for a few months, or pay a one time flat fee via PayPal. I would on the other hand be completely uninterested in making a series where a mod-creator wanted a percentage of the income I made, as I already have to spend enough time as it is to produce the actual content for my channel, and I have explained above just how difficult it is to get the accurate numbers, and also the challenge of "How long should such a deal extend?" applies.
As for content on YouTube, Twitch, etc - please also remember that the content there is offered freely. There is no paywall, and most game publishers obviously prohibit this kind of footage of their games from being behind any kind of paywall in their license agreement for their game - which makes perfect sense. Thus many people who watch YouTube content provide exactly $0.00 to the YouTube channel's income, because no ads shown = no income made. Also, I cannot and will not impose bad conscience in any of my channel viewers for using an AdBlocker. I am just happy that I get views on the content I make, and that people enjoy it, as that is a the very reason I chose to start publishing content on YouTube. Some YouTubers might attempt to impose a bad conscience on their viewers for using AdBlockers, but I am fairly certain that if someone did that, they would quickly lose a substantial amount of their viewer base, as if there's one thing I've observed in the YouTube community, it's that many people react very negatively to a content creator pushing the agenda of "I'm doing this for the money" vs "I'm doing this because I love doing it" (exceptions being someone who is upfront honest that they are both loving it and that it is their main source of income - most people usually reward honesty).
Finally - and probably most importantly.
The Factorio community have for as long as I have been a part of it always been one of the friendlier communities I've been a part of. I urge all parts in this debate, whether you are a mod-creator, a content-creator, a Wube employee or just someone who follows the debate, to please remember that we have one major thing in common: We love Factorio. This community usually works together to do amazing stuff, whether it's the game itself (Wube), the amazing mods (mod-creators), the series on YouTube (content-creators), the actual gameplay (the very dedicated and loyal players of the game). Please try to remember that in this debate, as I would hate to see schisms occuring between the various sub-cultures of this wonderful community!