This is interesting, and it brings up a rather subtle point about affordances. It seems to me that aggregation of people is not the same thing as facilitation of conversation. So, for example, Paper.li is an interesting way to bring in a diversity of points of view to one place where you can read and absorb it all, but it’s still essentially one-way.
Affording different types of educational conversation (small group, large group, one-on-one, intimate/private, public, etc.) is a much more challenging task. And to me, this is where the supposed PLEs that I’ve seen in the wild tend to break down. Either they are essentially aggregators and thus inadequate, or they end up blurring into the LMS space. I don’t think the latter is bad, by the way.