Accessibility is a different matter, not related to handedness - being left-handed is not considered to be a handicap. Adding accessibility features does not mean the team needs to include people with whatever handicap those features are tailored to though, they just need to gather enough input from people who need these features so they know what to implement. This does not mean the team should not include someone who happens to be blind (etc.), if that person is willing and able to contribute he's as welcome as anyone else.