Agreed Apple has a lot of experience in this area. Under the hood every iOS app is a fat binary, since ARM isn't just one architecture. Nor are the variants compatible with each other like x86/PowerPC. I just don't see evidence ARM is powerful enough currently to make the jump and allow a smooth transition (At Apple's quality/polish level). Nor can I see Apple being willing to drag this out across a multi year timeframe.
For PowerPC to x86, they had a clear transition path for every product. Low end went to Core processors. High end went to Xeon. They also were able to license the binary translation layer Rosetta (
it wasn't an in house technology).