Mostly I don't have the feeling they want to invest more into MacOS. I feel they would much rather push everyone into iOS, a locked down platform where they have full control on what people can do or not and monetize every single step (whether that is realistic or not).

I dunno, it seems a lot to ask to not fracture the entire desktop.

Matching the perfomance of 91W-class i7's found in iMacs would take a lot of ARM. 45W-class i7's in Macbook Pro's are quite powerful, too.

I mean they already did it once with the PPC->x86 transition with Mac OS X. This is basically Microsoft's Rosetta layer.