Hey.
I'm working on something similar.
It's based on REST, it only uses WebSockets to push changes.
When you open the app, the objects are loaded through REST. Now when somebody changes an object, a push notification is sent over WebSocket and it's automatically updated.
I would love to talk about it and about other possible solutions, so both of you guys feel free to contact me at vojto (at) me (dot) com, if you're interested. Thanks.