We should rather stop allowing sign ups without an application. The captchas are not good enough.
That’s near impossible to enforce, due to the federated nature. Server admins could whitelist which instances they trust, but I don’t think that’ll do much good from a community point of view.
Perhaps a sticky to find better moderator/timezone coverage could help. (And for that matter, I wouldn’t mind stricter moderation on post relevance - not all news about tech companies or events that just happen to take place online is tech news, imho)