There are a number of recent tickets about accessibility improvements in the admin, several of which raise questions that relate directly to the UI group. In particular:
#21283 Keyboard focus in the theme customizer should be on left options panel
#21310 Need skip link(s) at top of admin pages
#21312 How to log out of WordPress without a mouse?
#21324 Visible Focus within Admin Screens could be much clearer
#21326 Screen Options in Admin – Accessibility Enhancement
#21334 Accessibility of Quick Edit panel in Posts/Pages/etc
Please check them out and comment in-ticket with any feedback you may have; the same goes for any of the open tickets in the Accessibility component. Also, there are some tickets in the most recent batch that should be fairly easy for people who are just learning how to contribute. As always, you can ask here or in #wordpress-ui or #wordpress-dev any time if you need help with the whole process of working with trac and trunk, applying and building patches, and the like.
In general, we want to be keeping accessibility in mind with all UI work and working closely with the accessibility group. Major thanks to everyone who has been stepping up and raising these issues lately!