Dear MS (assuming you made the call), thank you for realizing people might want to buy content outside of UWP.
... Would I be pushing my luck if I hope Sunset Overdrive somehow magically appears on Steam someday?
You realize that UWP is not the same as the Windows store, right? UWP is just the idea that an application written for Windows 10 can also work on Windows 10 mobile without having to be ported to it. It can be released on the Windows Store, Steam or even retail disk.
So it being on the Windows Store was not it being a UWP application. It would still be a UWP application on Steam.
Windows 10 and Store are epic failure, so i am not surprised by this. A game should be on Steam from day one.
A failure? Its market share has increased in 6 months and is at about 25% which is pretty damn fast, especially compared to 8 and 8.1.
UWP is an attempt by Microsoft to sieze control. It is a self contained file system that provides privileged access to API's while isolating the files in a container whose contents cannot be accessed. In addition to this UWP is 'portable' but it is also locked down and while the method of distribution is largely irrelevant, it is controlled by Microsoft.
UWP also has significant limitations, firstly (and I'm not certain if this has changed) Games do not run in fullscreen, they run in borderless full screen mode, meaning the game does not lock the screen for exclusive use this can have an impact on render performance. It also imposes hardware restrictions too in that SLI is rendered useless in UWP titles; etc... It is not simply 'a method for ensuring that "application written for Windows 10 can also work on Windows 10 mobile without having to be ported to it"
UWP is simply an attempt to transfer control from the User, you cant peer into the UWP container and your ability to utilise hardware features of your PC is dictated by the container. There is also some concern that in the future Microsoft may deprecate Win32 in favour of UWP, now, while I doubt that Win32 is likely to disappear the concerns remain and they are valid. It is quite likely that feature development will favour UWP over Win32 moving forward.