Frankly it's harder to come up with examples where it's actually just a Pareto improvement that was undiscovered until considering accessibility. This isn't to say that this is not worthwhile anyway to make tradeoffs but claiming that tradeoffs don't exist is just magical thinking.

Some obvious examples (even ignoring higher cost, since they are all also higher cost):

* Coloring for colorblind people is worse for people with normal vision.

* Large format type is cumbersome for people with normal vision.

* Traffic signals that are long enough for the elderly to cross cost everyone time every time they are used.

* Stalls in bathrooms suitable for disabled people means fewer stalls can fit.

* Ramps for wheelchairs require way more space than stairs and take much longer to traverse.

Again, I'm not saying we shouldn't do these things.