If I had to guess what would be big, I would guess that it could be some sort of push technology [read: not http in its current form] Currently it's difficult to create efficient multi-user systems on low bandwidth and high data rates, with RSS clients pinging servers every three minutes to check for new content and ajax calls every three seconds to check page changes and do autosaves, etc, that is a lot of undue stress on a server. Developers will start packing as much data into a single packet as possible, doing micro-optimizations, while somebody else is going to come along and re-desgin the protocol. It could still use XML and Javascript in general, with some other methods to accept data pushed from the application server(s) [bittorrent anyone?], and not the other way around. It could be huge...but alas, doesn't exist yet.