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.