I'd build it somewhere in between what it is now and Usenet. One of the biggest benefits of RSS is how easy it is to publish content. Two of the biggest downsides is the lack of interactivity and the lack of discoverability. What if all of the rss readers spoke to each other? What if you could see which feeds people were reading? What if you could add a comment to a particular post and have a discussion with other people who are reading it? What if you could be notified of updates to certain conversations the same way you're notified of updates to your feeds? A killfile will solve the issue of not seeing unwanted content or people. Maybe go with a federated model instead of peer to peer, so that the servers could scrape the internet for RSS content. That way discoverability isn't just limited to what you and your friends are already reading. Maybe use Cap'n Proto as the app-to-app wire protocol instead of http for real-time updates.

> Decouple it a bit more from html

Is that really possible? I've considered it quite a lot in the past few years, but I can never get past the fact that it has become the universal markup language. Even markdown converts to HTML before displaying (so it can by styled with CSS).