So it's weird this post is becoming a thing now, after he demonstrably knows they're not (currently, at least) trying to do that.
Reading the parent post: "The risk here is that, if Microsoft convinces everybody to use UWP, then they phase out Win32 apps. If they can succeed in doing that then it’s a small leap to forcing all apps and games to be distributed through the Windows Store."
That's not a small leap, it's a huge leap. And this is an inherently fallacious statement. It's equating a technical one, swapping an insecure app format for a secure app format, with a policy one, blocking third party apps. When, as a closed platform, they could block third party Win32 apps if they wanted to just as similarly. They could make Win32 apps ship through the Windows store, and I believe they discussed it at one point. It's silly that he's particularly equating UWP, a security feature, with a platform lockdown, when the platform lockdown could easily come with or without that security feature.
And even if this imaginary reality of Tim's became real, we currently have two viable OSes that Steam works great on that aren't Windows. So Microsoft would have to weigh their perceived gain of a lock-in against the potential loss of the gaming community. Ubuntu wouldn't have a hard time attracting gamers if Steam support was solid, and was kinda broken on Windows.
That doesn't nullify the concerns that started this whole discussion, though: Microsoft could be pushing people towards UWP for less benevolent reasons, and surely has the technical and commercial capabilities to try to make Sweeney's hypothetical scenario the new reality.
Maybe this is just a mistaken perception, but I suspect Microsoft may have burned a lot more bridges with their recent actions than they have realised so far, particularly among enthusiast and "professional geek" communities that have remained generally positive about MS and its products for longer than most. Viewing anything they do with suspicion is a natural consequence of the way they've been treating their customers lately, and I don't see anything they do that has any hint of lock-in getting an easy ride from here on out.