It could have been answered in the Quality thread, but that alone has 41 pages already.
So, here is what made me go "/whoosh?"
So far, the 3 additions to the game mentioned in this post's title have been said to be separate mods. Since mods can be disabled, I figured one can play with any of these combinations enabled. This was stated in at least the Train or Quality FFFs?
In the Quality FFF it says that uncommon and rare are unlocked by the first research, quite early, just as the other tier one modules.
Epic and legendary are then unlocked at one of the first 3 planets, and the last one respectively.
Which makes me wonder. Can Quality even be enabled without space age, or is the latter mandatory for at least Quality?
Or is it as simple a shuffling the research tree around when Space Age isn't enabled?
To me that's the answer, cos I can imagine how you set up dependencies, having done some minor modding and reading here for 6 years now. But I guess it's not as easy for everyone.
Is this an oversight in planning or an oversight in communication (cos when it says where the latter tiers unlock, it doesnt say anything about my question?)
Like I said in that other little thread, I'd love a combined list of what's known so far, possible with some FAQs of the related entries. (/spoiler'd for easy readability?)
List of "mods" that get enabled when you buy the expansion.
List of free stuff.
List of QoL stuff.
Imho it would make things easier to find and could be a selling point for some.
I know FFFs since 2017, and they have always be awesome read, even when talking about technical stuff thats way above my head, but with an expansion on the horizon, I think there should be a more centralised point of information, this is a totally different beast.
Get the hype up!

*Elevated rails are a quite simple answer I guess, I just mentioned it in the title because I was cross reading said FFFs and forums on my phone which is a pain with tabs.