Oddbean new post about login | logout i think the relay would be a better place to fight spam. relays can choose to only store events with POW and/or from users who pay/have proven balance. then users select which relays they want to use.
I do think there's still room for data-driven methods that detect this type of thing. All the data is out in the open so anyone can build heuristics or algorithms for flagging non-human accounts, for instance. Those algorithms can then be open sourced for any relay operator or client to use.
This also doesn't require any changes to the underlying protocol