I'm just still not convinced that it can't be avoided because of following/unfollowing, ability to completely block users, as well as domains. Plus the filtering controls that do not exist yet but will.

The downfall, I think, would have to be comprised of two things. MASSIVE MASSIVE MASSIVE amounts of traffic resulting in an avalanche of new users, along with complexity in the UI design of Hubski's filtering controls such that they are not breathlessly simple and intuitive and apparent enough to the newest users to be functional and useful.

If Hubski can nail the UI for filters to the point where the newest users are aware of them and can use them effectively, then I think it'll be pretty good. The last great threat will be in the comments section of threads where, due to popularity, a massive horizontal influx of comments of low quality show up in numbers where it is too hard to block that many users (or the comments aren't bad enough to warrant blocking someone you don't know, but they are collectively 'meh' and uninspiring or otherwise not great).