One solution (not the only solution) will be web of trust. If my WoT tells me that Alice’s nsec got compromised on such and such a date, and her new nsec is whatever, then my apps will curate content accordingly. My WoT will do a good job because she’ll tell as many of her close associates as it takes to get the word out, and my WoT will have established previously who are her close associates. This is very doable.