The new 4.2.8 release is out today. It's a small update that introduces a mechanic that will automatically switch sign-ups to manual review if no moderators have been active for a while. This should reduce vectors for spam and abuse in the future.
@MastodonEngineering I love this!!!
look! 
@MastodonEngineering
Thank you!
@MastodonEngineering should add a feature to auto defederate an instance that falls to far behind in updates...make it configurable to set how far back you allow federation.
@MastodonEngineering I love to see mitigation that isn't something along the lines of requiring a phone number to register. Here's looking at you #bluesky.
@MastodonEngineering: is the mechanism disableble?
@MastodonEngineering The DeadMod switch! Very much appreciated.
@MastodonEngineering one caveat is that this would require those instances with no moderators to update mastodon, right? 
(mostly just joking, I follow that this is a forward-facing mitigation)
@CodingItWrong @MastodonEngineering How about a feature on all Mastodon servers where they will refuse to federate with other servers older than "N-3" (say). That would kill off unmaintained instances pretty quickly, forcing maintenance or users to leave. Sounds harsh, but that's the world we're heading towards...