I’ve been wondering when this would happen, since now that Apple does their own fabbing and that their A-series is nearly as speedy as Intel chips (from a user perspective — there’s no way a current ARM CPU can beat the top-line i7 chips yet), moving the Mac to ARM and regaining full control of their platform is starting to be feasible.
The scary bit is that it may well explain a lot of the hardware delays, as well as mean the end of the Mac as a fully agnostic development platform — so here’s hoping they won’t switch wholesale.