It was not the LLVM-optimized software pipe renderer, but the non-LLVM softpipe renderer, which was and will probably always be slower than the hand-optimized Mesa software renderer you already have builtin in Haiku.
You miss nothing here really, except the ability to experience it yourself
Adrian has already posted some comments on the haiku-development mailing list. It seems he's trying to reuse a former Linux Kernel Library haiku port to see if it could ease porting DRM and heavily Linuxy gallium drivers code.
Nobody can today say how far this path will goes or even if it will.
Sorry to break it, but no: there is no point for such task until we have at least some 3D hardware acceleration working.
Being there too, and done, well, not enough as I would want to improve that situation.