It's not an obvious win like the last couple of architecture switches because of the end of Moore's law. Like the PowerPC chips they were initially using ran 68k code quicker in a non-JITing emulator than any 68k they could buy. They had to switch to a JIT with Rosetta, but that same perf distinction was still true for the high end for PowerPC/Intel during their switch.
Running x86 code faster in an emulator than on a real chip might not ever happen.
And in not too long the x86-64 patents will have expired all the way through SSE4... I think Apple making their own x86 chips is just as likely as switching to ARM.
I'm sure they have prototypes and I'm sure they will consider releasing it if they have a design that works well, but I doubt that a laptop chip will ever be the focus of their main development team.
Isn't it pretty much taken as a given that Apple is going to produce an ARM powered laptop in the next couple of years?