Thanks so much for this, Jen!
Some work has been done in the 2.3 release, sponsored by the Canadian Museum for Human Rights, to improve AtoM's accessibility somewhat - we made some mobile/responsiveness fixes, and added screenreader support and better keyboard navigation for the public user interface. However, as you've rightly pointed out, there is a long way to go, and much more we could do to improve the accessibility and overall usability (especially on mobile) of the application. I hope we might be able to collaborate with our community and take on more of this work in the future.
Regards,