No crazy scheme like this will work, because creating any form of anonymous account is super easy.
What we need is to add a layer of trust assignment and authorization system based on reputation, like what Fediseer does but built-in into the application. Then we can quarantine new users, contain their actions until the admin gives explicit approval, auto reject follows if they don't have at least N trusted people vouching for them, etc...
It won't stop the people interested in doing mass-manipulation of votes. There is no virtual difference between a bot that votes through Lemmy and a bot that votes through "pure" ActivityPub.