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This rumour has half of my "prophecy" in place: 13" and 15" MBAs. The other half of my guess is this being Apple's first entry into the Mac market with bespoke ARM SoC/SiPs. As a result, lower prices for a Retina Mac which will continue to steamroll Mac sales as the WinPC market continues to falter.
ARM would destroy comparability with Windows x86 versions of OSX, and would obsolete huge numbers of apps. ARM is not ready to run OSX with decent performance.
 
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