I want to like and use Elm. However, unless things have changed recently, it seems the author hasn't learned to delegate. They also like to really get things right, which takes forever.

So it's really good at what it does, but for everything else, it's just incomplete. For instance, Elm seems like a natural fit for an offline-first ServiceWorker design. But I don't think it really covers much of the just-outside-of-core-Javascript browser APIs. You're likely to run into "I have some really interesting ideas about how to cover that a super elegant way, but I'm concentrating on rewriting the $WHATEVER right now" newsgroup posts, but that's it… :-(