The UMA Acceleration Architecture is derived from EXA and was supposed to be merged back into EXA, but that didn't end up happening. UXA basically takes the EXA API but internally now uses the Graphics Execution Manager for managing the memory. As our UXA benchmarks have shown, UXA is faster than EXA on the Intel Linux graphics stack, but it isn't yet completely stabilized and is rather common for people to run into screen artifacts, stability issues, and other problems. The Intel driver is currently the only one implementing UXA for its means of 2D acceleration.
In the xf86-video-intel 2.8 release candidate are various fixes (in particular, some for X-Video, UXA, kernel mode-setting, and various other areas throughout) along with support for their unreleased, next-generation chipset. Support for this unreleased Intel IGP is already in the Linux kernel and the DDX driver has picked up a new shader compiler and other features for this chipset simply known as "IGDNG" right now, or Intel Graphics Device Next Generation.
The complete list of changes for the first release candidate in the Intel X.Org 2.8 driver series along with a source download link is available from the intel-gfx mailing list. The final release of the xf86-video-intel 2.8.0 driver will likely come this month or next.