It's entirely possible to implement a wave like UI over SMTP. Many mail clients already implement thread views etc. If you take a step further and implement a threaded diff view it's already fairly close to wave UI).

While I like the the shared/synced document object model, I'm not sure about the value added via a new/unproven protocol stack just for the per character gimicks.

"Real time" is overrated and not needed in many cases.