I actually expect Apple to implement some "emulator-acceleration instructions" into their own chips and get excellent (almost as good, as good or better) performance once they switch, as always, because otherwise people just won't switch en masse.
If Apple make the move, I kinda expect them to do nothing, and make their customers deal with incompatible software. They've been super hostile to their customers of late.
I dont think Intel will allow that to happen without some patents issues.
x86 is now 30-40 years old depending on how you measure it. Even "modern" x86 (post Pentium Pro) is over 20 years old. An awful lot of the patents have expired.
X86-64, that is the most important one.
It's not even by Intel; it's by AMD and they did nothing to prevent Intel from using it.