This is similar to hashcash proof of work concepts that inspired Bitcoin. Use proof of work to make not traffic expensive, to create a financial disincentive for running the bot.

I'm curious to see if Tor users get impacted by this.

https://en.m.wikipedia.org/wiki/Hashcash

Is there something better than a CPU intensive task? They obviously are worried about the power consumption.

I'm thinking a memory and time intensive task that is minimally CPU intensive would be better.

Grandma's DSL router is about to get much warmer.