Originally Posted by TranquilTempest
It wouldn't be the first time apple has shifted architectures. If the past is any indication, they'll have a translation layer for backup, but they'll also use FAT binaries for a few years. It would most likely be easier than the earlier shifts, because they already have in house experience developing ARM processors, and have the iOS codebase.
I also think most apple customers don't base their purchase decisions on performance benchmarks. At least, they're not comparing it to PCs, they're comparing it to their old machine.
More realistically they will go with a hybrid approach having an ARM based processor for battery or lighter loads and firing up an x86 chip for legacy support or software that needs it. At that point it becomes a software and integration problem.
I could dream up some speculation involving an AMD custom design that uses chiplets providing x86, gpu and then somehow integrating apples ARM based chip on one package. Probably not realistic, but that would provide a platform I could get behind if it all worked seamlessly.