I don't think the right time to make that transition is while they're trying to switch to ARM. Right now, they're probably trying to get things switched by making as few changes as possible. That eases the transition for everybody. I'm not sure why they would want to deal with both things at the same time. They are both huge undertakings. Not to mention, the two things are really unrelated. Besides, how does CPU architecture affect the ability to lock the OS into only running App Store apps?