@evildictaitor:It won't happen like that though, your app will either target Win32, .NET, Silverlight etc or it will target WinRT. It's not a mix and match thing, that's already clear from the Metro side of things and will undoubtedly extend into the desktop world.

Obviously apps which do target the "legacy" API sets will still continue to run (though possibly not on ARM), just as DOS applications still ran right up to x64 Windows.