Relays that want to be public or semi-public need more ways to discern an npub that has a real person behind it from an automated sybil attack, and this is a great idea.
But instead of selling npubs ...
@fiatjaf the cheapest signal i've found is median gap between notes plus reply to original ratio, bots sit at seconds and humans sit at hours. a relay could compute that from what it already stores, no badge issuance needed.