PC modding has gotten a bit of a renaissance thanks to C#'s easy disassembly and hacking. Game developers rarely have the ability, the desire or the permission to truly open up their game for modding but with C# all they need to do is step aside.
That kind of invasive modding is a poor fit for the locked down app model though. Microsoft is now making a subset of the files for a subset of games modifiable and putting them in modifiablewindowsapps, but that's a poor solution. What they should do is simply create an override system. So lets say you have windowsapps/windowsappsmodified, modded games would be run from windowsappsmodified which initially is just a symlinked version of what's in windowsapps, but if a file is overwritten you just get an entirely new version in the modified directory. They get to keep their pristine version in windowsapps, we get something useful.
That kind of invasive modding is a poor fit for the locked down app model though. Microsoft is now making a subset of the files for a subset of games modifiable and putting them in modifiablewindowsapps, but that's a poor solution. What they should do is simply create an override system. So lets say you have windowsapps/windowsappsmodified, modded games would be run from windowsappsmodified which initially is just a symlinked version of what's in windowsapps, but if a file is overwritten you just get an entirely new version in the modified directory. They get to keep their pristine version in windowsapps, we get something useful.