How about adding context (e.g. similar to wordpress's category tags). People can then filter the streams they subscribe to.
For example were YouTube to post an OStatus message when a new video were uploaded I could subscribe to GeekAndSundry@youtube.com's messages, then filter that subscription so that only those posts with categories TableTop and TheFlog came through, without seeing posts tagged DarkStarComics.
Equally, if a user posts about their two hobbies, say Technology and Cycling, I could filter to only see their Technology posts, reducing a lot of the clutter in my feed.