About baking x86 emulation into ARM
No need to do that. AMD can simply manufacture a double quad core. Four x86-64 cores and four ARM cores. Running on ARM exclusively most of the time, running x86 code emulated if needed, and switching on x86-64 cores only if more performance is needed. The only problem is cost, I don't think such a CPU would cost less than $100, and that really precludes all low-end segments and much of midrange, too.
Biting the hand that feeds IT
