@jwz @SomaFMrusty I don't see why it would have to mean recentralization, as much as having some admins who would be willing to be spokes / regional hubs to a certain range of other sites.
Every large global social media site is essentially decentralized, in technologically meaningful ways that generally boost performance.
My comment re: Memcached was merely that yours was the kind of problem it solved. But if it can be solved efficiently in ways that don't drive users crazy, I'm all for it.