Hi, fable-elmish author here. Elm is great if you don't care about investing into two ecosystems or don't have a backend, or don't have a Native client in addition to Web, or don't care about what JS ecosystem has to offer.
Fable lets one use F# for both frontend and backend, and being able to share the code (models in particular, but really anything) while maintaining clear separation of tiers reduces your code base and dramatically improves quality w/o the need for elaborate tests.
Fable-elmish lets one use the same frontend code and architecture to write Native and Web apps. Again, YMMV, but at our company being able to transition an entire team between completely different types of projects avoids expertise silos and makes truly cross-functional teams possible.
We have OSSed a lot of our backend tech that helps building event-driven system in F# as well, in case anyone's interested: https://prolucid.github.io.
As Tomas said, just like Lisp in Paul Graham's "Beating the Averages" has been his secret weapon, F# is ours.
There is a way to develop for UWP with F# - MS' own React Native support + Fable. Write your app in F# using Fable React Native bindings, transpile to JS and deploy to UWP.