Hey @LegionnaireLenny
I'm enjoying your SpeedUp mod and have an idea for a UX improvement.
Aside: I mentioned you in the starsector discord, I'm @dismiss42. This post ended up being much better formatted, however if you wanted to have a discussion about these ideas before bothering to implement anything it would make sense to do so on there, perhaps?
I'm often in a sort of DDR keyboard game double tapping shift, spacebar, capslock .. trying to get the intended timescale. Does not help (not your mods fault) there is no feedback at all when pressing shift, if the game is paused. Actually .. If you could get the game to do the same hud text message and radio click sound when pressing shift that you hooked up for capslock, that would be
great.
So anyhow here are two alternate control layouts for you to consider, avoiding the double-toggle paradox

"Engage"
Each key is for setting a specific timescale.
Example: F1, F2, F3 for 1x, 2x, 3x (shift is unused).
"Throttle Up/Down"
Example: +/- to adjust throttle from 1x,2x,3x,4x (shift is unused).
One good thing about avoiding the shift key is that it is by default used already in combat and having different controls for timescale while in combat vs out is endlessly confusing. Final thought: since the game offers no ui feedback as to the current timescale, and I for one will not remember, I'd recommend treating the pause key as also "reset to 1x", however I'd need to test that out to be certain it would work.