Not centrally, no. But many existing P2P networks prove that you do not need massive data centers to hoard everyone's data. You can use the collaborative effort of humanities existing computation devices.
That was not the point he was making -- he was making the point that "even with facebook's amount of traffic, you could host it on a dozen servers". That is just so far detached from reality I cannot take that seriously.
I agree that p2p social networks are an interesting alternative, but they are a whole different kind of product and a kind of apples / oranges comparison in terms of cost of operation.
Decentralization is less efficient. Instead of each piece of information being copied in a few place it would need to be copied to hundreds or thousands with a decentralized system.
Decentralize all the things.