> I'm concerned that after all these years, it's still a separate project and not an effort sustained directly within the kernel mainline and mainstream distributions

What does this mean? Hardware support is rarely developed inside these organizations; what makes it seem like these groups would be a good home for this effort?

It makes sense to have a group of experts in a field (Apple hardware/firmware) contribute patches upstream, which is the exact system here. And Asahi have done an above and beyond job also maintaining their installation framework while carefully moving changes upstream as well.