It was obvious to me, knowing that MacOS is based on NeXTStep and how that ran on a bunch of different architectures—68000, Intel, Sparc, etc.
I even wrote 3 years ago here on HN (before Apple announced their transition to ARM) that I wouldn't be surprised if there were ARM-based Macs in the lab [1].
And also knowing that Apple always wants to be in control of as much of the technology they rely on as possible. After Motorola/IBM dropped the ball with PowerPC and Intel couldn't deliver the performance per watt they needed, they weren't going to fooled a third time.
No, the porting is obvious - I guarantee Apple has test rigs running Darwin on AMD processors and RISC-V, for example - but switching, as in, actually doing something with that portability, is less obvious.
