Ian has been working in a branch of Mesa with what he calls the "Assembly Shader Rework" and rewriting the ARB program parser and adding in support for NVIDIA layered extensions. His hopes were to get most of this ready for Mesa 7.6 and it looks like this will end up working out right on schedule.
Announced today on the mesa3d-dev list is word that Ian will be merging the asm-shader-rework-1 branch into Mesa's mainline Git tree today. In that announcement, he's reporting that some tests have sped up tremendously as a result of this reworked 3D code. So far though this code has just been tested with the software rasterizer and the Intel i965 driver.
Mesa 7.6 is shaping up to be an interesting release with this new work, new Gallium3D state trackers (and even network support), more Radeon 3D features, and many other improvements.