And the interesting question is : given decentralized censorship, or even no censorship at all, what sort of community can emerge from that ?

My impression is that 4chan is resilient from becoming a failed community, because they have no particular goal, except maybe every one doing what pleases themselves on a personal basis, given it doesn't bother everyone else.

Any single individual will, pretty naturally and unwittingly, act as a moderator, out of personal interest. 4chan is like a chemical reaction that has displaced itself towards equilibrium. It won't move easily one way or the other now, and so it'll remain as it is, 4chan. But just what it is, and what sort of spontaneous equilibrium can happen to a community, remains to be seen.