That's one of the least-plausible Microsoft trickery ideas I've heard of. Anything that makes Mono play catch-up also hurts every existing .NET program.
Even if they had some magical changes that kills interop (like, what, I don't know), Mono still works with all current apps at that point, and only developers adopting the new, not-compatible system (and thus discarding all their old libraries) would be affected.
Microsoft sorta has done this, with Silverlight and WinRT. They required different stdlibs and a bit of runtime tweaking, as I understand. Silverlight was handled by Mono, and WinRT - not sure if anyone is interested, as it's really for Windows Metro applications.
Even if they had some magical changes that kills interop (like, what, I don't know), Mono still works with all current apps at that point, and only developers adopting the new, not-compatible system (and thus discarding all their old libraries) would be affected.
Microsoft sorta has done this, with Silverlight and WinRT. They required different stdlibs and a bit of runtime tweaking, as I understand. Silverlight was handled by Mono, and WinRT - not sure if anyone is interested, as it's really for Windows Metro applications.