If appstore was part of every app and the appstore license only covered the appstore part and not the whole app, then that would be an improvement.

But I think it would be easier just to not have apps covered under the appstore license, and only add such license to their own DRM. How effective the legal DRM would be in that case could be discussed, but it would likely identical to consoles and tivo which are both gplv2 compatible. It seems unnecessary when looking at other products with DRM to have a license that cover every program running on them.