I don't see how that makes much sense, business-wise.
The Mac is a stagnating business (like all desktop and laptop computers). Custom made processors won't persuade anyone to switch back from phones and tablets to a somewhat legacy class of devices. So being dependent on Intel is just fine from this perspective.
For their mobile devices on the other hand, it made all the sense in the world.
Also designing a really fast and still efficient processor is hard. There were once a lot of CPU makers around, but pretty much everyone else apart from Intel and AMD have given up creating mass market computer processors. Because it didn't make sense, business-wise.
There are a few initiatives for ARM server CPUs, but so far they have been mostly remained promises. What is on the market is not convincing and disappointing, and it's uncertain if it will change.
Sure, Apple can do it, but it will cost them a lot of money.
Also, Windows won't run anymore or only with a lot of drawbacks. There are plans for an ARM Windows with x86 emulation, but that's going to be a huge pain. Lots of things won't work, new drivers for everything will still be necessary, and it's pretty unclear if there is even a market for it. Microsoft have already failed in their first try (Windows RT) because no one needed it. Games will still need an x86 Windows because the emulation will be too slow, so those won't definitely run on an ARM Windows. Microsoft isn't Apple, they couldn't pull this off even if they tried really hard.
And of course, all the Mac software has to make the transition, too...this will probably be the easiest part. And it's still annoying for customers and might drive some away instead of attracting new ones.
So in short, it would be a highly risky move with totally uncertain outcomes and little benefits even it everything works well. And for what? The future lies elsewhere.