TL;DR
There is a lot that could be improved with the replay system; surely it wouldn't hurt to take a look at it again... Here are a few ideas I came up with:What ?
FreecamShould be easy enough. There is already a dropdown for which player to follow, so why not have one for no player at all!
Toggleable mouse forcing?
Not entirely sure about this one, but maybe it would be nice to save mouse keyframes so you can have a more convincing replay that includes mouse movements if wanted.
More control in general
Let us look around in the gui! Let us zoom in and out! Surely there is some leniency that could be afforded?
I don't want to go through a 58 hour long replay at slower than 64x speed more than once please don't make me have to! can you tell this is why I decided to make this post
Add an option to add savestates or something at certain points. It shouldn't be that hard to just save the starting position and copy over that portion of the replay. With a good ui I'm convinced it could be made to look non-jank.
Higher speeds..?
Maybe there could be something similar to https://github.com/emlun/factorio-replay-timelapse, but you know, more robust as it is in-engine. This could easily scope-creep out of control so I will leave it at that. It's certainly [way, way] easier to come up with ideas than to actually make them.
Please don't forget about this feature
I don't know how well it copes with multiple surfaces, but with Space Age looming, I think we'll get to know soon. Please please please make this feature work better in the context of Space Age.