The main thing that RSS lacks is any notion of push (i.e., a traditional pub/sub model). A student and I worked out a clever solution to this, he built a complete working prototype. See also, Open Microblogging.

In short, what you want is a whole lot like an RSS feed, but with additional infrastructure to handle timely push notifications. And, while you're at it, how about decent crypto for authentication, gossip protocols for scalability, and on and on.