Yeah, founded a startup based on this idea in 2006 or so, called WeBrowse. The technology wasn't quite ready although I got pretty far with a prototype based on DOMMutationListener and XHR.<p>Pretty clearly something like this needs to exist, and it will probably not be nearly as useful as it's inventors think it will be. Screen-sharing is more general, and the niche for low-entropy real-time synchronization of browser state <i>feels</i> pretty small right now. But who knows? Heck, I thought the iPad was going to be a giant flop.
Cool! I do agree this concept is under-utilized. Best of luck!<p>(Heads up: if you shall ever venture to patent this tech, I think I'll be able to present compelling prior art from like 1996. This was also a proxy-based re-writing mechanism for co-browsing and from your description it does sound kinda similar. It also happened to use HTML frames.)