Maybe make it hidden to the public (like Koala Wallop's Octagon) and invitation-only, with any given member limited to one invitation per hundred upvotes they've received?

Or... a nested thing, maybe. The onion has as many layers as the Grand High Administrator deigns to create, and said administrator can initiate anyone to any desired depth, or revoke such access, at will. A given user can issue one invite to their current layer per 100 net upvotes they have received on the layer in question; when someone receives 100 net downvotes on a given layer, they are banned from that layer until reinvited (at which point they start from scratch). Invites to a given layer can only be directed to users who have already been initiated to the layer immediately outside that one.

There might also be a branching structure; nobody knows for sure until they find parallel layers.