There were some noises about allowing Win32 on it at some point, but those mostly died down and at this point it's Universal Apps only.Wait, do all of the games on the Windows Store come in the form of Metro apps? Oh god.
Oh god indeed.
This applies to some things but not others. For example, a dev could never offer true fullscreen or Freesync support in an UWA app even if they wanted to. And as a matter of fact they also couldn't offer Mumble support, because you can't interface with outside (non-sandboxed) programs.To me it seems like all those "immposible" things come down to inability to fix those things post-release, and not the game dev's inability to implement them.
Meaining that those things are possible, but they need to be done properly by the game dev rather than be fixed by the community after the game is out.
But even if those restrictions for developers themselves were not there, the ability to interface various programs with each other and for the community to improve and extend games well beyond the original support of the publisher is part of the identity of PC gaming and has been for decades.