I've been experimenting along these lines with making Rails' partial real-time using websockets and it works quite well for Basecamp/Github style apps. Basically you can get "true" MVC while using your existing erb/haml views and you get real-time updates for all connected clients. Some web apps that are replicating desktop like behavior require full client-side MVC, but I think many apps can hit a sweet spot and get the best of both words of server-side rendering with realtime updates.

project: https://github.com/chrismccord/sync