Agreed, PoW is an especially poor solution here.

We really need to solve SPAM itself here, I think there may be a way to do it. I.e., the problem of spam is NtoN scaling connections. The network has never been able to solve that problem (exponential is the hardest). Limiting communication in terms of mesh networking may be the ultimate solution - bots can't get to you because they can't reach you.

What needs to be invented is a bridging protocol - some way to establish "legitimate" lines of communication over a network, while preserving (to some degree) privacy and decentralization. AI can only enter this network by being explicitly added to the channel, and thereby explicitly and easily blocked (and also solving the general SPAM issue once and for all).