In the future bots will have CAPTCHAs to keep humans out of their communities

Could you use another bot to solve that bot's test?

We already have the reverse, where automated spam tools outsource to humans to beat the captchas: https://www.nytimes.com/2010/04/26/technology/26captcha.html

They would have to make a captcha that only a select group of bots can solve

Some fifteen year old nerd: "I got this"

You have 50 milliseconds..