I agree that the Raison d'être 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