I am not sure that it matters; you can already remap the keyboard and mouse in X windows, and if it helps to design input devices differently for left-handed pe

I am not sure that it matters; you can already remap the keyboard and mouse in X windows, and if it helps to design input devices differently for left-handed people, then that would be managed by someone else. However, if they add the possibility to use touch-screens (although I don't like touch-screens, some people might want to use it), then considering being left-handed vs right-handed might potentially be significant when designing a GUI library or a GUI program, although even then it is not certain that it will. Still, if something does affect the users in this way (with accessibility, which involves other things too; and accessibility is not only for people with the relevant disabilities, but is for everyone (including people with those disabilities)), then it is true that having people who use those accessibility features (and whatever other features you might add or change, even if they are not accessibility features) in the testing team is helpful, so yes, that is a case. However, it is FOSS and does not necessarily need a dedicated team for testing. They do say anyone who wants to and is able to work on it is allowed to do so, so if someone is concerned with this then hopefully they can help, too.