In this hypothetical situation Microsoft doesnt make the stupid move of requiring all apps go through their store which imposes its own limitations (like sandboxing).
Mind you, it would be a completely insane move for Apple (or Microsoft) and I can't see them doing this any time soon. It would be absolute suicide.
How is Adobe going to do it when Windows follows the same footsteps than Mac OS X?
The only way will be the store, or why do you think Microsoft is making it easy to port Win32/WPF (legacy) applications to the store model?
When the applications that matter like Adobe are on the store, and Apple has proven the "my way or the highway" works, they will slowly disable the "legacy" model.
I have been through enough computing changes to believe this will indeed happen.
Mind you, it would be a completely insane move for Apple (or Microsoft) and I can't see them doing this any time soon. It would be absolute suicide.