I think the future of these decentralized networks is to make it trivial to set up and run your own instance, in much the same way as Napster allowed anyone to host a file streaming server. The problem with the current system is that new users must choose an instance in which to create an account, so they will tend to choose one of the larger ones. A better idea might be to have a few large instances only for user accounts with the rest of the functionality distributed automatically across all users who sign up to host.
These are just the thoughts of someone with a very basic knowledge of distributed networks and I don't know if it's even doable.