Looks like a decent implementation of HashCash - great! They should implement TOTP-based nonce generation to avoid the need for a database entirely, that would

Looks like a decent implementation of HashCash - great! They should implement TOTP-based nonce generation to avoid the need for a database entirely, that would make the system much more lightweight to deploy. Some people miss the point of this. If you and another person are running away from a cheetah (fastest land animal) then you don't have to outrun the cheetah to survive, just the other person. The same is true for sites getting away from spammers. They will go for sites that are easy to attack before yours, so as long as the effort outweighs the outcome you're safe. It doesn't matter if the solution isn't perfect, it's better than nothing, and if it's not widely adopted it's not worth the effort to bother cracking.