Nothing is being moved. UWP has been here since the dawn of Windows 10, which evolved from WinRT, going back to Windows 8, and is constantly being extended with new APIs.
I've been holding of targeting UWP, until proper F# support.
I have experience with plenty of languages and technologies, including C, C++, Rust, Scala, OCaml, Haskell, Clojure, Elm, Idris, WinForms, WPF, DirectX and dabbled with Silverlight. Migrating from WPF or Silverlight towards UWP shouldn't be a problem.
F# has been my favorite language since 2008, but the hostile anti-UWP, anti-Windows community, compounded with the lack of abstraction features such as ML functors, higher-kinded types, type-classes and terrible modern Windows client support, are driving me away from it.
UWP is pretty mature now and all modern default 1st party Windows apps and critical UI components such as start menu, action center and settings rely on it, and more is being migrated towards it all the time, there is no sign of UWP going away anytime soon.
Except for Windows Phone getting killed, which was the _main_ device type for UWP. The Windows app store is the same graveyard that it was in late 2015 when the announcements around new Windows Phones piqued my curiosity. It looks like that's simply not a thing anymore. I'm betting my money on Xamarin and the browser for a client application, not UWP. There's just no point to it.
UWP is the future of Windows APIs, in case you missed Windows Developer day earlier this month.
So if F# doesn't speak UWP, the community keeps tweeting that GNU/Linux is so much better than Windows, and that we enterprise devs just don't get it, should we bet which of those technologies will last longer on MS roadmap?
My F# code runs on Linux. My client code is migrating to the web and mobile, as is just about every enterprise in the US. Why would I watch Windows developer day?
The main device type for UWP is any Windows 10 device. See the list of benefits mentioned in the link above, which extend beyond phones. I've never owned a Windows Phone, yet I always prefer UWP apps.
Also there is a big market for 2-in-1 tablets, and new small Windows on ARM devices are coming out very soon.
Not every kind of client app is suitable for the browser, especially if you care about performance and deep native platform integration. And I'd rather not deal with JS frameworks when not targeting the web.
It's nice when you're where the cheese is currently at, that's not what I'm talking about though.
I do hope for your sake you don't wind up in the next lifeboat after the Silverlight crew, I really genuinely do. Good luck!