The OS X on ARM rumor (already running in a secret laboratory) said it could become under attack. Believe it or not there is even new software written for x86-64 today for instance Yosemite. The PC market is shrinking but its far from being legacy.The market portion consisting of customers who have to run legacy Windows and apps written in x86 asm was never under attack. That's for Intel, AMD and Via to fight over.
That day may never come. Other CPU manufacturers have always been cheaper than Intel, creating an incentive for PC manufacturers to replace them if possible. Still INTEL managed to fight off AMD and maintain their margins with performance gains. But ARM represents another kind of thread, to fight off ARM they need to make progress in energy consumption. And they did.The portion consisting of customers running portable software (which includes almost anything built with Xcode, gcc or even LLVM under Linux) will go under attack if and when vendors can ship a 4.5W TDP 64-bit ARM CPU that is either close to competitive in performance or a lot cheaper to make or buy than this sub-GHz Intel offering.
It's not enough progress to counter attack ARM in the smartphone and tablet market. But it's enough so that fanless notebooks will be energy-efficient INTEL computers, not high-performance ARM computers. And INTEL will earn good money with this monopoly.