Some kind of federation for hashtag follows is what I’d like to see the most. Currently I am using a larger instance mainly to get a good chunk of the traffic for the hashtags that I am interested in. The ability to filter content for user follows would help in this area too. I want to be able to follow a user but only see their posts with specific hashtags.
Oh, and markdown support! Really miss having a proper way to do lists, literals and code blocks.