Apple could give the people the power to 'unlock the phone to a certain level' and allow to install the external Apps they want. But with an "Only On" switch, with a time stamp and disabling every major iOS security feature like Face ID, Touch ID, iCloud, Apple Services, and even their own Store, CarPlay, etc.
Before enabling 'external mode', show 2 or even 3 warnings in RED and with a slider at what cost they can 'unlock' this feature, and the only way to restore original 'closed Apple ecosystem' mode would be restoring the phone to factory settings asking help to an Apple service.
All will be happy and pleased: power-users, standard-users, IT staff (so they can block corporate apps if the iPhone has this option turned 'On'), the technocrats around the world, and Apple himself, that will can remind everyone that they lost all their security but could be back at anytime they want with a Genus Bar pro help (with a little service fee of course).
Folks, I have solved it.