If keys get hacked there’s no recovery.

But I see what you mean, eg someone I follow gets hacked and turns spammer?

What about a 24hr block?

I log in and see 5 people have temp blocked me? Huh? Maybe someone I follow has become a spammer?

Lots of nuance that could be added, but the simplest rule set is to serve a whitelist of all my followers followers.

Everyone would have a unique whitelist and they would shift organically all the time.

It would also promote good behaviour within the network. Potential loss of reach for bad behaviour.