Firstly, this is a really nice project! It's very clean, loads quickly, and pulls things into the feed within minutes of something being posted :) But there is some functionality that would be super nice!
Tagging, folders or groups - It would be really nice to be able to split feeds into different sections! Like having your youtube rss feeds seperate from your news sites. Making those groups collapsable as well would be amazing.
move it up, move it down - Moveable feeds is kind of part of the past suggestion, but I felt it deserved its own section. Easily being able to promote feeds up or down the reader would make it a lot easier to customise.
That's about it for the moment. Again, I really like this project and these ideas are "nice to haves" :)