LLILC is absolutely interested in upstreaming and in fact, at least one big change (prelim COFF support for MCJIT) is already upstreamed (http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-...) in addition to a few smaller ones.

Diffing upstream with http://github.com/Microsoft/llvm will let you track what Microsoft is currently doing in its repo.