Presumably Apple isn't going to redesign their GPU architecture every generation? How much maintenance do you see this needing?

Uhh... Linux supports a lot of hardware. Probably a lot of in-tree drivers that still get use were started as reverse engineering efforts by a small number of people.

Perhaps you're meaning to say Apple will iterate the hardware faster than people can add Linux support? That's plausible. It also was the status quo of Linux on PCs for many years. (Still the case with some hardware I guess.) That hasn't killed Linux yet.

Maybe someone else will also pick up some skills from this. He is streaming all his reversing sessions on Youtube, it is quite interesting.