While Hubski could use some more traffic at the moment, I think there would be a certain point where the feel and quality of the site would deteriorate dramatically with the form of Hubski as it currently exists.

The problem with reddit's growth is that there is now a very large number of redditors that came late and share absolutely no interest in what the early generations of redditors had. For many, reddit fills the role of memebase or funnyjunk or some kind of personal blog. More provocative content is getting edged out of the spotlight. Whatever the trend of change is, it will only continue in that direction as time goes on.

What makes reddit able to cope are subreddits. If you ever just want to throw in the towel with the current reddit, you can just migrate to the more insulated specialty communities where people have formed them for that very purpose. Now you also see major subreddits taking action to enforce a certain bar of quality, so the issue is widely acknowledged.

If you haven't seen it, r/theoryofreddit has a lot of this kind of talk.

I think Hubski has some policies in place to deter the kind of deterioration reddit has seen, having learned from its predecessors. But I don't think Hubski has built-in elements to cope with the change if it happens like reddit does.