I'm of two different minds on this proposal.
PRO: I kinda like the idea, because it seems self-balancing and gives players choices. I really, really don't want to do captchas though. Captchas are a big annoyance unless you find a way to make them fun? Because they are NOT fun.
CON: It seems like it will rely mostly on the good faith of players, botters and botting service providers. Are there consequences to botting in the human league? How severe, and how do we prove it? Bot Utility Tokens on an account is a convenient tool you can easily use today, but there is no reason they are necessarily held on the playing account. If I ran a bot service I could simply allow a user to stake 2 tokens on any private "management" account, and run two other accounts undetected using posting keys. If bot services think they can operate discretely, then the players pool will have given up half its SPS, and still might find itself playing "secret bots" without tokens.
So I might flip flop on this.