I actually think Apple could find a way to navigate it. They already allow one prominent alternative choice on iOS: non-iMessage SMS. If Apple allowed third-party stores, I could see them using their product, UX, and branding mastery to create the equivalent of the blue-bubble and green-bubble dichotomy for App Store vs. 3rd party downloaded apps. Creating a social stigma without technical restrictions, so to speak. So allowing an alternative while at the same time encouraging users not to partake in it.