Hey fiatjaf, I was thinking about this, what if a relay uses its subscribers for content rating (zaps boosting only) and thus over time only stores those messages with the most zaps and likes? This way the relay is dependent on a majority of the subscribers to make a decision, but only a boosting decision.

Boosting might be done on the relay side, because it involves actual money incentives, and filtering may be done on the client side.