That's the intention of the wiki page: http://trac.roundcube.net/wiki/Dev_AccessibilityGuidelines
Cool.
I emailed Thomas about this but im working on a full rewrite of the keyboard shortcuts plugin. This new version will allow for user-configurable keys and for other plugins to register key-selectable events as well. (as an example, use a key to report a mail as spam). This seems to augment the work Thomas is doing with keyboard navigation, but time will tell. Once I understand what I need to be doing im fine with making that plugin follow accessibility rules as well.
Maybe some of the core plugins could become showcases for how to implement accessibility in plugins.
Cor