SharpDX has already made that worry go away, it has very similar APIs, more flexibility to harness deep graphics techniques, and is open source.
Xblig will stay how it is and ppl can try their luck for the near future, but smart devs would look into SharpDX Unity etc to cover their bases
Windows 8 app store will make the Xbox indie marketplace look outdated , it could even eclipse xbla...
Kind of didn't answer though... will games become unplayable?