Personally, I feel like it makes more sense to just have each server be its own instance without hosting the other servers content and instead have the user identity/account dettached from the content servers (something like OpenID to have a common user account across services). Then use standards so a common UI can be used client-side or for any particular server-to-server communication (much like how blogs can do backtracking between blog posts from different blogs and so, without them really having to federate). It would be more efficient while having the same end result but with a more free and open ecosystem, like the blogosphere used to be before it was shadowed by twitter & facebook.

To me, federation between private servers the way mastodon does it only makes sense for private communication like XMPP or Matrix… but the minute you are publicly posting content in the internet it makes no sense to have servers mirror the content from others just so people can access that content from one server in the next… if redundancy was the point then it would make more sense a P2P model, if a common UI/account was the point then separating those would make more sense. The current structure creates a dependency between the user and the server that hosts your account, the content being public forces the instances to whitelist which other instances they allow, and this makes it so you might end up having to create multiple accounts in different servers if you wanted to access instances that do not want to federate, and at that point it’s not much different from centralized services. It restricts what instances the user can access (based on which instance they are registered with) and places extra responsibility and bandwidth/storage requirements on the instances themselves.