So far as I can tell, there are three groups of people with an interest in llvmpipe. (1) People with newer technology the FOSS drivers haven't caught up to yet, mostly ATI customers; the ATI driver lag time is shrinking and looking fairly good right now for basic 3D accel. (2) People with ancient hardware by defunct manufacturers that don't want to pay $50 for modern-ish AGP card; screw 'em, these be computers, keep up or shut up. (3) People with oddball hardware, mostly netbooks and tablets and the like, that come with video chipsets not designed or supported by one of the Big Three; usually very weak CPUs on these puppies.
From what I've seen, the biggest group of people wanting/needing something like llvmpipe were the ATI customers with r600/r700/r800 parts. r600/r700 is pretty solid these days, and r800 is wrapping up, and will probably be ready to go around the time the 3D desktops are more than just an upcoming plan.
I am totally ready to be told I've gotten it all wrong here, though.