^ This is incorrect. Cortex is a brand name for ARM's own CPU designs, just like Snapdragon is Qualcomm's. Apple, Qualcomm and ARM all design CPU's based on the same ARMv8 instruction set architecture. In that sense it's exactly the same as installing W10 on a x86 or amd64 based system.
The differences between these company's mobile SoCs have little to do with the ISA. The differences stem from all the other subsystems built into a SoC (radios, gps, media processors, DSP, etc).
W10M could be made to run on, say an Apple A9, but this would require that new drivers be built specifically for that hardware configuration. I don't know if Apple provides the technical documentation that would be necessary for developers to build such drivers. I suspect not, which means only Apple and MS could build such drivers in a reasonable amount of time. That won't happen anytime soon. So, while W10M running on an iPhone is technically possible, it's highly unlikely to become reality.