I see your app is GPLv3 but I don't see any exception in there for Apple, nor do I see any mention of a release for other developers to sign before accepting pull requests.

The vanilla GPLv3 is incompatible with Apple's App Store and they have pulled GPL apps in the past as a result. See: http://www.zdnet.com/article/no-gpl-apps-for-apples-app-stor...

Here's an example of a work-around that would allow you to retain a copyleft license and continue to distribute your app on the app store: https://github.com/WhisperSystems/Signal-iOS/blob/master/CON...