Could MS be trying to compete with JVM in letting people to create new languages targeting the .Net CLR?
That's already possible.
Also, these compiler APIs are language specific, so they don't actually help with that. (it's sort of interesting to think about what a more generic take on this, or a subset of it, would look like, other than the CLR itself, though).
edit: I think my grandparent poster was being ironical, since if you know what the CLR is you probably know what it stands for ... right?