I think given the aims and limitations they've set for this it's a reasonable proposal and it will likely meet those objectives. As mentioned it will work for s

I think given the aims and limitations they've set for this it's a reasonable proposal and it will likely meet those objectives. As mentioned it will work for smaller botnets but larger ones will still overwhelm individual clients in terms of resource availability. Personally I dislike proof of work, it's basically bloat as a defense mechanism in this case and can obsolete older hardware fast while consuming in aggregate probably a lot of power across the devices it affects. At scale it would be quite a large environmental burden. I also think a lot of attackers will consider it a success to get it to that high difficulty as users who have to wait 1 minute of their device being 100% pegged will probably choose to disengage a lot of the time. That said it's quite a good way of mitigating DOS attacks while not doing anything to compromise user anonymity, so from that point of view it's a good solution despite the drawbacks. As it exists on tor, I don't have too much of a problem with it but I'd consider it a total disaster if applied to the regular web.