It is a little hard to see where development is going:
is EXA a one-for-one replacement for XAA, or just for some use cases?
Is UXA a replacement for EXA, or a branch of some ideas that will be remerged?
Surely 99.999% of graphics implementations will be one of Intel, Nvida, AMD/ATI and Via (I've not come across anything else for years now, and certainly not one which allows you to use multiple adapters).
Is there a case for streamlining X down to EXA/UXA and drivers which support one of those....?
I've rootled around on xorg.freedesktop.org, but can't really find obvious answers to these sorts of questions.
Users of, say Matrox, would probably be pretty content with the feature set of Xorg 7.current.