Didn't Microsoft say that they're working on fixing overlays, mods, vsync, higher framerates/gsync & freesync though?
Vsync is already available on some games (has to patched per game).
Gsync/freesync. Well gsync already worked in windowed mode, it just didn't seem to work with some win10 games. Support for freesync/gsync has apparently been added to games now, but again seems to be a per game thing.
Mods. No. All Microsoft has said is "depends on the mod". Or in other words, developer sanctioned mods only.
http://www.pcgamer.com/microsofts-uwp-will-support-some-mods-but-not-all/
""The mods where we’ll probably have some discussion, is... if I go in and change the executable in a way—if I actually go in and reorder the code or inject code paths the developer didn’t originally intend, [then] the problem is, I don’t know if that modification is to fix a broken game, or to add some kind of phishing tool to the game so that now it’s capturing my passwords as I’m typing them into Chrome."
high hz/fps support. It was never an issue with them not supporting it. It was a specific issue with killer instinct, something that could have been user fixed on a normal win32 app, but not on UWP, and had to wait for a dev fix.
Overlays, no. All they have ever said is "working on support" followed by it's fairly simply for devs to port it.
Just as with the xbox one launch promises, all the answers MS give are vague "it's coming, it'll be supported", but never any details
Anything that hooks into the .exe or uses injection is unlikely to ever be supported due to it being unsecure (see the paranoid "capturing passwords") excuse.