I haven't, I'm curious to know whether it has transparent, type-checked, client-server RPC calls like WebSharper? Hands down must-have from my perspective.

As for declarative UI development I had worked with Formlets -> Piglets -> UI.Next and felt they had nailed it at the end. I haven't worked with Elm, my hopes are high. The only other thing I know likely has a good model would be: https://github.com/calmm-js