Hello,
Can you please give us a bit more details on how to try out the gnukhata demo? It appears I don't know how to login. Or do I need to create my own organization in there?
Bootstrap has accessibility plugin and I think it gives you some nice accessibility related things for free. Such great accessibility to Roundcube is only possible because Roundcube developers have implemented some custom keyboard navigation via _javascript_ where it makes sense, they have made their app well structured and yeah, it feels awesome.
There is another project built on top of bootstrap which is almost fully accessible. That is a social platform named Known
.