RSS is great. Recently we've added a RSS stream to our companies website tracking all changes. So now anytime somebody modifies an article or an outsider posts a comments, it shows up in my News agregator. It is just example how a relative simple XML based protocol with enough support, allows us to build complex, cross-server systems. It allows the consumer of information to postpone the unavoidable moment of information overload by agregating information from different sources. No need to check a website every week for something new.
But it has its limits. Some of these limits stem from the fact that RSS has developed in close relation with the whole blogging thing. Others have more to do with missing components. For some of these problems solutions exists, but they are immature and or not open and therefore not widely adopted. What follows is an overview of what is missing.
If I subscribe to a blog, my agregator will try to retrieve the RSS anything from every 6 hours to every 15 minutes. If a blog becomes popular, this means that the amount of traffic spent on RSS becomes a considerable cost to the owner of the blog. Services like Bloglines help, but it would be good if RSS readers would, like bittorrent for example, automatically rebroadcast what they just read to other readers, this way spreading the load. Otherwise we'll punish the popular broadcasters.
Even though the RSS system is perfectly suitable for point-to-point distribution of information, in practice, people tend to subscribe mostly to the most popular blogs. This is perfectly normal and indeed the power distribution seems to be universal. But still, people subscribe to blogs they know, not necesarily to blogs that have the best content for them. A relative simple system would allow subscribers to vote on blog-posts and work out based on my votes and other peoples votes, what other posts would be relevant for me. (People who like this post, also liked...)
RSS is very much a one way street so far. People subscribe to your feed and they receive your posts, but there is not much of a protocol by which they can let you know what they liked and what they didn't. Sure, they could post comments, but every blog system implements comments in a different way. Why not embed in the RSS a series of callbacks, stuff that people can do with the posts, such as quote them, read them, comment on them or forward them for example.