In other words, IRC? Every "next big thing" communication medium has been trying to replicate the IRC experience for the past 15 years.
Twitter is the closest, it even has # and @ modifiers - I mean come on, this is getting pretty ridiculous. A stand-alone twitter client that shows a message from everyone that is posting to #topic and @messages directed to you? Last time I checked, that's IRC.
Pretty soon all of us will get our childhood wish and everyone in the world will be on IRC.