To support decentralization and spread, should lemmy.world close registration at some point to prevent a performance overload due to too many users? Of course, if registration is disabled, there could be a hint placed somewhere near that from other instances you can interact with content on lemmy.world just like you had registered on it. There could be a link to join-lemmys instance overview.
I honestly think during the sign up the registration to a server needs to be randomized to spread the load. That and allow the user counts to be global and not just to your instance and you then have user load balancing.
If we could also migrate our data between servers with a backup server option. When lemmy.world goes down, just switch to a different randomized backup server.