Captchas are not only for stopping people with disabilities anymore. They also stop people using non-approved browsers, people trying to stay anonymous, people coming from the wrong geographic areas...
If the AI has access to a credit card, but Mgulu from Nigeria doesn't, then the system doing the filtering might evolve to filter out the 'undesirable' rather than the non human.
Parasites can solve captchas, people with accessibility issues and the poorest of people are the one being locked out.