> why would Apple invest the R&D resources to create and support ARM based Macs when Macs are such a small part of their revenue and profits?
They already invest a lot in the development of their ARM-based processors for iOS. I don't think the additional investment for making them ready for Macs would be that high. Take the 12" MacBook for example. I can even imagine they could simply stick the current A11 processor into it and it'd be fine.
> Would they make more money by selling ARM based Macs?
They would still have to develop their own custom thunderbolt controller, an emulator, etc.
The only thing changing as far as cost would be the processor. Let's say they save $100 on the processor (not likely). They sell about 14 million Macs a year. That's only $1.4 Billion - pocket change to Apple.
They already invest a lot in the development of their ARM-based processors for iOS. I don't think the additional investment for making them ready for Macs would be that high. Take the 12" MacBook for example. I can even imagine they could simply stick the current A11 processor into it and it'd be fine.
> Would they make more money by selling ARM based Macs?
Yes. Profit margin would be much higher.