Earlier quoted context omitted.
As an administrator of an online message board, I concur. Web content is being so efficiently aggregated that some forums turn into the awkward conversation between two redditors: "Check this out!" "Heh, yeah. I saw that." Communities before were usually separated by platforms , because the platforms were not yet sophisticated enough to support vast communities of varying opinions. Now we have a few big players that…
In my opinion, such a platform, or several, using an entirely different paradigm, already exist. To overtake Facebook, it is simply a matter of making it as easy to use as Facebook, and Facebook annoyances having reached a breaking point. Whether there is yet sufficient impetus to do the UI work and whether Facebook users are ready to move on to the next thing is another question.
It's called Reddit.
Bear with me here, I realize this is probably an unpopular opinion.
On Reddit, all content is open -- I don't think I've ever seen a 'closed' sub-reddit available only to members. I'm not sure it's even possible.
Yet, in spite of all communities being effectively open, most sub-reddits have a strong sense of community, and are very active. Personally, I really enjoy proggit and r/math for this reason -- active discussion, community moderation, and a strong sense of community.