There's a lot of custom rendered stuff there. The problem with that is, without a lot of work, custom GUIs are completely opaque to screen readers and other accessibility tools.
I've started working on this. I'm not really ready to loudly announce this yet, but you can check out my plan and what little code I have so far (really just data structure definitions) here:
https://github.com/AccessKit/accesskit
Edit: I'll be spending next week working on a prototype, so I'm confident that I'll soon have something real to show.