You may be interested in intercooler.js (http://intercoolerjs.org/). It allows you to perform a host of AJAX + DOM manipulation flows using only HTML attributes.

intercooler also supports something similar to the server pushed DOM diff flow you envision:

Server Sent Events BETA (http://intercoolerjs.org/docs.html#sse)

"Server Sent Events are an HTML5 technology allowing for a server to push content to an HTML client. They are simpler than WebSockets but are unidirectional, allowing a server to send push content to a browser only." http://intercoolerjs.org/docs.html#sse