I hope we're smart enough not to say "Apple will never do ______".
I'm sure that Apple has a lab with OS X running on ARM, and any other processor out there - just to see how performance is impacted and how it affects various products.
Given that, will Apple do it? Who knows. One would like to think they learned from the Surface debacle (not to run two processor versions), but it's not out of the realm of possibility - especially if they're considering a new product category - maybe going back to a Consumer/Pro model.
I could even see them expiramenting with duel processors - ARM for low powered tasks and Intel for high powered tasks, possibly in a Powerbook Duo type of product.
In the end, Apple's going to go with what makes them the most money and is right for the largest portion of their audience. And there will be happy people and angry people.
I like your idea of a dual-cpu model! Perhaps basic applications that support execution in both environments, like editing documents etc. that might make use of the low power processor are possible.