I'm surprised with Windows 8 back in the day when they basically threw Windows Store closer to the Windows OS's core, M$ didn't try to quickly go the Apple route to lock their OS down to just the Windows Store for digital game-stores.
Microsoft did, more or less, kill Securom and other DRM's on their Windows 7 & above OS's (unless you use some of their work-arounds), right? They could do the same to Steam, if they feel like it.
The day M$ decides to flip the switch to basically render Win32 app's useless so those app's don't work anymore and/or that those app's are buggy as hell to basically try to kill Steam to the point that Windows Store + WUP (Window Universal Platform) is the only game store-front + game-client in town on Windows - that'll be the day M$ will really hurt Windows and both dev's/pub's & gamers will finally make the move to SteamOS.
For years, gamers been sticking w/ Windows b/c they (Microsoft) have a strong-hold on the OS Market b/c there are already so many games are already available on this platform (and still work) for especially the past; the present; and likely there'll be games there in the future as well.
If M$ gives gamers + dev's/publishers reasons to either ditch Windows entirely b/c they want to be the only major Digital Game Store in Windows Town and/or to dual-boot Windows (for old games) + SteamOS (for newer games), they'll do it.
Don't be foolish, Microsoft.