Jason Snell, on the whole ARM+Intel thing:
If you were to list Mac functions that might be offloaded to an ARM processor, Power Nap would be a good place to start, especially if macOS were tuned to be more aggressive about putting the system to sleep.
What would an ARM-Intel hybrid Mac look like? Would whole segments of the operating system run on the ARM processor, allowing the more power-hungry Intel chip to be put to sleep except when it was absolutely needed? There are a bunch of big questions here, most notably the identity of the code that would run on the ARM processor and where it came from. Would Mac apps include extensions or plug-ins that would be designated to run on ARM? Would Mac apps provide two separate sets of program binaries so that the system could switch them between processor architectures at will?
PowerPC to Intel was clean and fast; this sounds anything but.