This is cool. I've written two or three implementations of 9p in the past, the more the merrier :) In the other direction, I ported Ocaml's interpreter to Plan 9. Wish there were more people using it back in the day, but that's what you get from a dying operating system...
That's right -- it'll negotiate 9P2000.u if it can and otherwise drop back to 9P2000. I don't think it'll ever support 9P2000.l the very Linux-specific variant.
9P is cool though. Simple, elegant, working.