Re: ARM vs x86?
The OS is already ported - not only is iOS over half of OSX's codebase running on ARM, but there have been persistent rumours of ARM MacBook sightings for a couple of years, and Apple would be mad not to be running those experiments. OSX was on Intel for years before the switch in chips, so they have form. They have iOS on Intel experiments too - the dev emulator runs on Intel with native executables.
The trouble with going to ARM chips in laptops is that even the latest gen is slow compared with what we have now. Unlike the PPC to Intel change, where the Intel chips could emulate PPC code as fast as - or even faster than - the previous generation of Macs, ARM chips would run Intel code at ~quarter native speed. Crunchy, and Apple are highly allergic to crunchy UX.
And iOS on a laptop would be a horribly crunchy experience. I've used Windows8 on a nice 10" touchscreen laptop, and I've used an iPad Air with a nice Logitech keyboard case. They were both reasonably unpleasant halfway houses, neither laptop not tablet. I'm really not seeing iOS in a laptop form at all.
The point of jumping would be (a) power consumption, which Intel pretty much already have in hand for laptop class chippery, but also (b) moving the CPUs in-house, which I'm sure Apple would love to do. The groundwork is all in place, going ARM64 was one of the last required steps, but it's a couple of years and a couple of chip generations down the line yet.