I easily see the Air and Mini switching to ARM.
I have to disagree. I can see it happen, but I think it would be pointless, messy and bad business.
First of all, Apple has iPads for those not needing a computer's power - there are lots of accessories and keyboards for them and I've seen quite a lot people using iPads with bluetooth keyboards. Those not needing a laptop would stay with the iPad, those needing both would go with OSX Macbook, cause what's the point in having two low power gadgets...
Also selling ARM and Intel MacBooks would be very confusing for customers - ARM MacBooks wouldn't run OSX. If they would run iOS than the iOS would have to be redesigned to work with touch and trackpad. Therefore it wouldn't be iOS per se. Same goes for OSX - it would have to be some other version of OSX adapted for the new architecture. Putting all the software/compatibility issues aside, that would be horribly confusing and would result in a messy Samsung like portfolio. That's not very Apple
As for the 12" Macbook Air - I don't see that coming. Having 12 and 13" laptops, both with retina screens would be good differentiation. Customer needs crystal clear variants.
I think Apple could and should make an 11" Retina Macbook and have:
7" iPad Mini (Retina)
9.7" iPad Air (Retina) - I hope they will come up with some logical iPad naming... iPad, the new iPad... iPad Air... Seriously? Even I got confused at one point

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11" Macbook (Retina)
13" Macbook (Retina)
15" Macbook (Retina)
Whether they're called "Pro", "Air" or just "Macbook" is a lesser issue, because this way Apple has a clean-cut portfolio that's easy to navigate for customers - it's a fairly easy decision which Mac to buy:
light Macbook with longer battery life for simple tasks
"normal"/standard computing power, but still very portable 13" for more advanced tasks when you don't need superb graphics
15" top of the line beast that can handle almost anything you throw at it for real professionals and rich people
Apart from that (it's probably the customer in me talking now), they should up the storage on those higher end models:
11" with 128GB standard
13" with 256GB standard
15" with 512GB standard - I mean, you're paying a ********* of money for that computer. It's a premium, top of the line machine and they wanna be cheap with storage? Same goes for Mac Pro - $4000 higher end model with 256GB? Are they serious?
So that way they have multiple differentiating factors for each machine among which the screen size, processors and storage are the most eye-catching, thus directing the customer towards one of the models.
Anyway, that's how I would see it.