For lower latency, use JACK.
Keyword: drivers not the entire X.org by itse;f. Unity is a complete mess coding side. Remember commercial games often requires hardware accelerated driver like proprietary Nvidia or AMD CatalystGraphics drivers - Don't ship broken graphics drivers. I mean really... Replacing X.org will help, but I actually think the biggest part of the problem is Unity.
using OpenGL 3.x and above. mesa recently support OpenGL 3.0 since release 8.0.
Possible on Fedora. I do not know about Ubuntu.Input devices - Give us the ability to remove mouse acceleration - easy, simple, fast. Hardcore gamers will flock to the platform because it's a killer feature. Better driver support is of course a must but actually... Linux is pretty good here already.