So if I understand this right, you pick a server and your server account can post on that server and any servers that that server federates with.
So what happens to your account if the server you joined goes down? Yes, you could always create a new account somewhere else, but you lose all your followed communities and post and comment histories as well.
There should be a failsafe for this because as this grows, you’d also have a lot of servers which are not feasible to maintain anymore and thus they’d go down. Maybe an instance dedicated to archiving could work. Other instances could refer to that archive in order for users to migrate without losing their settings.