Today I hacked together a prototype using WebSockets for data transfer, just to see how much it would gain - and the results are impressive! Over my high-latency line (~120ms ping) using http caciocavallo-web was barely useable, using websockets there was only a slight delay. Even moving internal frames arround felt almost smooth.
So it seems after all the work there is a chance for it to be more than a nice demo =)
Unfourtunatly by hacking the prototype together, almost all of the existing stuff has been broken - and it will require some serious refactoring to integrate it smoothly. But for sure it would be worth the effort :)
Now it's up to the html5/browser guys/girls, to finally spec WebSockets and implement the missing features like binary data transfer.