That would solve the bot issue to some extent, but that would mean that everyone who wants to play has to get wax, probably do kyc at some exchange etc. instead of just registering with social media accounts.

I also thought about how I would implement it but couldn't come up with a decent decentralized solution.
Only allowing .wam accounts solves it for now, but I and I think also the developers don't like the solution as that means they only allow one centralized type of accounts.

Their first PoW approach could've worked too, but their benchmark was an inefficient single-threaded JavaScript implementation. Increasing the difficulty and improving the implementation would also help.