Detecting spam is the trick. New npubs could have a probationary period until "vetted". WoT-based lifting.
In general, the incentive ought to be to create content with which other trustable npubs want to interact.
Bots will always create multiple npubs, so a simple blacklist for spam isn't enough.
That pushes the filtering burden onto the best/heaviest users, tho, which will push them off the relay. Only useful for an onboarding relay, or something.
We could set up a charity for an onboarding relay.
Also doesn't solve for the sheer quantity of volume over the connection, which will eventually explode. It is not yet clear who is paying to throughput and manage the traffic and the servers.
