Accessibility needs to be regulated. In UK accessibility is well regulated for public websites: https://www.gov.uk/guidance/accessibility-requirements-for-p...
If we do not do the same for all websites then people with disabilities will be kicked out of a normal live.
> But how effective can this be?
As you point out it will not stop pirates.My guess is that they implement the feature, piracy goes down the week it is released, and everybody gets a bonus. In less than a month piracy is up again as they develop new tools, and people with disabilities lost access to it. But it is too late.
Accessibility in websites need some kind of evolutionary pressure to exists. Otherwise change after change it disappears. And the population that needs this features to have normal lives is not large enough to create an economic incentive.