Grrr. Why won't Microsoft open the CLR? It's so fast and has such amazing codegen! I don't want performance to degrade moving from Windows to some platform that requires I run mono!
While it's not the same insanely-optimized JIT-compiled runtime implementation that you're asking about, note that the .Net micro framework has been released as Apache 2.0.
Watch how you are about to answer your own question.
> I don't want performance to degrade moving from Windows to some platform that requires I run mono!
Yes, but Microsoft, who sells Windows licenses, does want performance to degrade when you move from Windows to some other platform.