[EgregiousCube]

+1, user owning the ID is a step in the right direction compared to "homeserver" owning the right key and makes this possible.

That said - maybe (total hypothetical) the reason one relay becomes really big is because a lot of people think it provides really good service, and maybe it's difficult to convince the majority of the network to route around it. This would create a similar problem to what we see in more well established federated chat networks.