Apple's Cyclone Microarchitecture Detailed
Apple almost certainly have a MacBook Air based on one of these chips at prototype stage.There are many reasons in favour, including keeping negotiations with Intel over price interesting, but probably the main thing preventing them running with it would be an inability to manufacture the chips fast enough, which is a major concern in mobile land. This is why lots of Android devices exist in variations based on different chips as hedges by the device manufacturer on long term availability.