Yes. I meant specifically something like old Skype authentication servers, sharing identities via ActivityPub. So that one person is registered on one server, another on another server, but they'll both find each other in contact directory and will be able to communicate.
But that's only for contact info, the actual content of the network should be decentralized and not stored on federated servers. Again, like old Skype (in the point of division between what's centralized and what's not).