Vlad Savov, writing for Circuit Breaker:
Intel already let Apple down once with the original MacBook’s underpowered Core M processor, and the absence of an Intel Skylake upgrade for either the MacBook Pro or Air this year also seems to have been caused by Apple’s dissatisfaction with Intel’s CPUs. There is nothing that Apple would like to do more than rid itself of its reliance on Intel, which would eliminate such unforeseen hiccups in the future. Apple is famous for its vertical integration, owning and controlling every possible aspect of its supply and production chain, and switching to its own processor chips across all devices would be the next logical improvement in that integration.
If you want to develop the next great processor, you’d better be going mobile first and building from there. Intel’s decades of futile attempts to shrink desktop chips into mobile devices have shown how not to do things. Now Apple’s persistent and apparently accelerating performance improvement with the A series suggests it might have found the right path through. It’s fitting that this new chip is called A10 Fusion, because the path it’s leading us on will eventually lead to the merging of what we now consider two distinct classes of mobile and desktop PCs. As Morpheus once put it, "it is simply a matter of time."
As with Mac OS X being compiled for PowerPC and Intel chips, I wouldn't be a bit surprised if, sometime in the next 5 years, Apple says macOS has been running on an A-series ARM chip in some lab in Cupertino.