There's a story going around about Apple working on ARM-based Macs. In other words, Macs that, instead of Intel chipsets, use the same kind of Apple A7-style chipsets found in the iPhone and iPad. The story is nothing new. ARM-based Macs, touchscreen Macs, iOS Macs, Retina Macs... Apple prototypes pretty much anything and everything any reasonable person would expect them to. A thousand no's for every yes requires a very high prototype to product ratio, after all...
It's fun to speculate — would an ARM-based Mac run iOS or OS X? If the former, could it emulate the latter so it could run OS X apps? If the latter, would it be powerful enough to emulate Intel to run apps not ARM-ready at launch? How would Windows Bootcamp be maintained, if indeed its still a desirable feature to offer?
There's even more to consider than there was when Apple prototyped "Marklar", the Mac on Intel project that ultimately resulted in OS X 10.4.4 Tiger.
Not everything prototyped makes it into production, of course. For example, Apple has been vocal about not liking the ergonomics of touchscreen Macs. It should surprise no one that Apple is stating an informed opinion, one of experience and insight gained from first-hand testing and experimentation. That's how Apple's works. That's how they make great products.
Apple hasn't said anything publicly about the pros or cons of ARM-based Macs, but it's likewise not hard to remember the conditions that led to the Intel switch and imagine there'd need to be similarly strong reasons to warrant an ARM switch. Unless and until that happens, unless and until Apple shows an ARM-based Mac on stage, the what is far less interesting than the how or the when.