Just a few moments ago I pushed my asm-shader-rework-1 branch to Mesa master. This fixes a couple minor bugs compared to the existing ARB shader assembler, and it improves performance of the assmebler by ~50x. We (Intel) are entering the bug fixing phase of our Q3 release, so I probably won't work on phase 2 for another month or so. When I do, I plan to add support for NV_fragment_program_option next. I'll follow this with support for a couple of the other Nvidia assmebly extensions.

This work has even been mentioned on Phoronix.com.