Do we really need 10s of millions of people here???!
Having gone through the time when AOL first allowed its members access to the Internet, the impression I ended up with was that it was exactly having the sub-culture of the time overwhelmed by the vastly larger culture of the AOL members that mainly screwed things up.
I think the desire for massive crowds is just a reflection of what we’ve become used to in the last couple of decades rather than the conclusion of thinking it through.
Mind you, I’m not saying that I have the answer, I’m trying to throw out there the idea that maybe in a forum of forums system “the more” aren’t “the merrier” because the sweet spot of participation to make a forum pleasant is somewhere in the middle rather than more always being better.