I agree that the Raison d'ętre for a .NET or JVM backend is interop. Perhaps that's not worth the effort of an entirely new backend. JavaScript is a different beast, however. I said before:
>From my point of view, languages that cannot run on one of the 3
> aforementioned platforms will become irrelevant. (with the exception of C,
> of course).
I'll take that one step further and say that for web applications it is becoming increasingly difficult to justify using a language that WILL NOT run both client and server. JavaScript (with NodeJS), Clojure (with ClojureScript), and Dart are just a few examples.
I really believe that with a solid JavaScript backend, Haskell would be an ideal web application language. Am I alone in that belief? What can I do to get the ball rolling on that?
--J Arthur