The CLR/CLI is one thing. The Framework is something totally separate.
Microsoft has submitted the CLR/CLI (along with C#) for standards approval.
And I think the Mono project has a great working implementation of the CLR.
However, all that pretty much means is you can write an app that computes
2+2 and have it be cross platform. The Framework on the other hand is a
bunch of classes... most of them simply wrappers around the Win32 API.
Porting them will prove to be difficult I suspect. Though I hear the Mono
guys are making great progress. But, without Microsoft lending their full
weight behind it, I doubt it will ever happen.