Unladen swallow: accelerating Python

I don't think that using LLVM is starting from fresh.
It has been used by Apple in their graphics pipeline from OS X 10.5
It's the future of some linux drivers as well, known as gallium3D. I think it has already been merged....

Or from the horses mouth... http://llvm.org/Users.html

I'm not saying it's the best or wisest choice. I'm not qualified to do that ;) - just that it's far from starting on a fresh.