I suspect they will offer different apps. The official one on the app store becomes limited or doesn't change at all. The app released via other stores will be Zuck's wet dream of a Hoover of all your things. There will be no limitations on tracking. There will be no limitations on what parts of the system can be accessed. Even if the OS puts up road blocks, Zuck will just ask the user for permission and they will all be granted. Even if it is something the official app store would ban from publishing if they were accessed.
Do you honestly believe they wouldn't? If so, I have a bridge for sale