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 think apps should contain the ability to create an account, and select a server at which that account is created. Maybe they could sort the servers by distance depending on country or something.