Your analogy of a "carefully crafted echo chamber" is, I feel, a fantastic one for what the actual goal of Hubski is (at least from what I've gathered). I think that means that quick changes and "flitting" between subjects are not really in the scope hubski. If you want to follow along with #detroit, you must carefully expand your echo chamber to include it. You'd have to comb the threads and choose the users who will best represent your interests. While tedious, this avoids a group-think mentality. Instead of everyone being forced into a common echo chamber (for example, a subreddit), each person crafts and maintains their own. It's more control ceded to the users, with an even flatter playing field, and I'm digging it.
I've just joined Hubski less than an hour ago, and realized that /that/ is how Hubski handles things. It's not a Twitter clone, nor a Reddit clone. This prevents group mentalities like 100k subreddits, but I am interested at how it deals with users with massive amounts of followers.