I've been thinking about this a lot lately. An invite only platform where invites need to be given and received in person. It'll be pseudonymous, which should hopefully help make moderation manageable. It'll be an almost cult-like community, where everyone is a believer in the "cause", and violations can mean exile.

Of course, if (big if) it does end up being large enough, the value of getting an invite will get to a point where a member can sell access.