Woah, so it looks like we agree, and this explanation is a long way from "nope vs. yup", thanks.
Before thinking about the technical elements of ARM vs. x86, I thought about the precedents at play. First, at the 2005 WWDC, Steve Jobs proudly demonstrated that OS X had been, in secret, developed for both PowerPC and x86 and that the company would quickly transition to using that architecture for all of its products. Second, Lion appears to be the beginning of a trend towards unifying the mobile and desktop OS X experience as much as the differences in screen size and input method would allow.
While I don't think there'll be an all out transition from x86 to ARM, I think that unless Intel does relatively better than IBM did in getting more performance per watt, in the medium term, especially with Apple pouring development dollars into iOS and the in-house development of the A series, an ARM powered device with a keyboard and a MacBook Air type form factor makes some sense. It also dovetails with Apple's MO of having more and more control over the devices by creating a reasonable premise for locking this hypothetical device down- it's more iOS than OS X.
Also, this could light a fire under Intel to enhance Atom (or to scrap it and build something altogether better) and to lower the already preferential pricing that Apple receives.
This is of course all speculation from someone who knows much more about Apple's product line than the x86 or ARM instruction pipelines, so, thanks for reading.