On the other points I agree, provided the (likely) policy of not accepting distro specific patches.
XMir *kind of* works on my R600. It's slow as hell (seriously slow, far slower than software rasterizer on an older computer with X.org), but except for Mir's cursor freaking the hell out of me, it worked. The fix for the extra cursor was reported to be in the works yesterday, and was tagged as critical. I'm not sure how should I report the performance problems, or how to give measured, maybe reproducible, numbers on the performance that reflect what I'm seeing. I'll look into it, but if someone can give me directions, they will be welcomed.