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.
It’s not hard for Lemmy to grow at all. Use a different server. There’s no upside to being on a crowded server. Join a fast and reliable server. Hit “all.” Done.
Lemmy is designed to grow easily.