Hi,
We had some helpful AppleVis members assist us in refining the VoiceOver experience in our app Soundproof over recent weeks.
I wrote an article about this explaining how we treated some of the custom UI elements and interactions to make it as good as we could. It might be useful to some of you:
http://transition.io/going-deep-with-accessibility-in-soundproof/
We'd still like to improve the app's VoiceOver support further, but what we have now is pretty good. The most frustrating part is the seeming inability to stop VoiceOver announcing a button or other item when something changed and you actually want it to announce a more important item. Hopefully we'll find out how to do this safely in future, or Apple will add the ability to do this if it really is missing and I'm just... missing it.
Cheers