I like this idea of using tags instead of distinct boards. I don't know if there should be a limit to the tags. People could vote on tags, the more votes a tag has the higher the score / weight of terms in search.
Maybe there could be some sort of content curation feature, create themed channels that consist of posts that you create or add to favorites. People could subscribe to either a user's channel or the user altogether. The difference would be that by subscribing to a user you could choose to subscribe to everything they post and/or every channel of theirs.
Just some things off the top of my head, would like to know what other people think.