An advantage that Twitter has over RSS is that Twitter can provide real-time streaming, where RSS requires an app to check a feed at intervals (setting aside PubSub and RSSCloud). With Twitter making itself worse all the time, I think it’s worth seriously considering other approaches (like micro.blog). Running a web-wide streaming service is expensive, though. I wonder if real-time streaming could be faked within an iOS/Mac app using CloudKit. Each user’s app could check the source once an hour (or so) and then update the public CloudKit entry with its findings. If you have 60 users, that’s one update/minute. 3600 users means you get one/second. Many users wouldn’t have 3600 followers, but you’d get the popular accounts in near real-time and others would at least be updated more frequently than standard RSS polling might achieve. Plus any post made from within the app could be sent up to the system immediately. Just a thought.
Edit: And of course there’s no reason it would have to be CloudKit. A client could easily talk to a different server and tell it it’s found a new item in the feed. Point being, you’re using crowdsourcing to keep a feed updated.