Intel SNA is what most of the xf86-video-intel driver changes have been about since this 2D acceleration architecture was introduced back in 2011. SNA is the pet project of Chris Wilson at Intel's Open-Source Technology Center and is the one responsible for a majority of the work.
Even after two years of work, it still hasn't replaced UXA as the default acceleration method, although Ubuntu 13.04 is defaulting to it for Intel hardware. After all of this time, SNA is still an active work-in-progress.
Committed today to the xf86-video-intel driver is the latest work. Chris Wilson is now experimenting with a threaded renderer for fallback compositing. This threaded renderer is for fallback purposes and uses pthreads for supporting multi-threading when falling back to Pixman for image compositing.
There were also other work committed today and yesterday, including improvements for the SNA back-end affecting the old Intel "Gen2" and "Gen3" graphics hardware. Another change was preferring to use the BLT ring for vsync'ed copies on Ivy Bridge and future hardware, plus a variety of other technical advancements.
The ongoing "Sandy Bridge New Acceleration" architecture improvements to xf86-video-intel can be monitored through this CGit query. Maybe in 2013 we'll finally see SNA replace UXA as the default 2D acceleration method.