Whoa, that's cool!
What do you think about Typescript? I mean it's unsound but - it sounds like an ok compromise
Didn't use TypeScript, so can't say much. I guess some types are better than no types, and it's easier to use for JavaScript developers.
Personally, I'd prefer a fully typed language.
Ur/Web is not very practical for reasons other than type safety: the lack of libraries and slow compilation when the project gets big. The language itself is good, though.
Nowadays, I would probably choose OCaml. It doesn't have Ur/Web's high-level features, but it's typed and compiles quckly.