[yew]

Not sure that's so far from Haskell, really... :-P

Maybe it's my lack of experience talking. Haskell feels heavier in a lot of places. I think the focus on compilation in the backend is almost a downside here, too.

Can it be in isolated places? That's doable...

Depends on the application. There's a lot of hardware out there that does really weird stuff. There's some interesting work in Haskell-space (eg Atom) but I don't know how comprehensively mature it is.