I've thought of creating a social network that groups people into small groups of 100 or so, by interests and location. I would advertise it as a chance to escape the monoculture and explain that the cost if you must participate a minimum amount, like 1 post or comment per week on average or something. And then you could mix up the groups every year or two. It would have its pros and cons, but it would achieve the goal of letting small groups form and create their own cultures. It would also succeed regardless of its size, so long as you have enough users to form a small group.