I must say this is one of the well-documented add-ons as far as source code is concerned. A note about object presentation type at the beginning was really helpful, too.
Regarding license: I understand that this add-on is licensed under GNU GPL 3, which is incompatible with GPL 2. Have you considered re-licensing the add-on?
Subsequent to the publication of the add-on dev snapshot, there has been a discussion on the users list about using native interface versus an add-on like this (see the NvDA list archive for details). The only thing I would add is that at least give folks a chance to demonstrate their skills with an add-on like this - who knows, it might be useful for some.