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.
At the early stages no. It is vital we keep it open to get as many people through the door to promote fediverse. Eventually some people will create accounts in other instances.