Yes, this is not a theoretical possibility, but an inevitable move. I expect the NIP for it any day now.

"Relays can publish 'blocklisted' relays (because blacklist is racissss), and other relays can query them."

At that point people just set their relays to query other relays for the untouchable, shunned ones and automatically block them.

Somebody could bang that code out in like half an hour.

At that point it's important to make relays really cheap and easy to run. That's where Nostr wins over activityPub...