The answer is: it depends. They will silently bend the "TRC" a little if there is a business case for releasing something now and not later.

But most of the requirements center around nitpicks of software polish: Specific words and phrases used to discuss the device, loading screens must not just be a black screen, the game should not crash if the user mashes the optical eject button, etc. These things add a level of consistency but aren't the same as "solid 60hz" or "no input lag". The latter sort of issues can be shipped most of the time, they just impact the experience everywhere.

No, Carmack isn't a fan of Linux as a gaming system. Look it up. Which is to say, on the consumer end. idtech was coded in NEXTStep workstations until at most quake 3, so he liked Unix for development. IIRC, the linux ports of idtech were done by Dave Taylor, not Carmack. Carmack basically just gave a shrug and signed off on them, because they worked, so why not?

And RMS's hell is one where everyone uses open source to some extent, calls it open source, and has no philosophical reason for using it, only practical ones, and have no qualms about mixing it with closed source software.