Apple already went through this before with PowerPC -> x86. They had universal binaries, Rosetta, etc. to build off of. And they got to do it with their own hardware, which includes some special instructions intended to help with emulation.

> Apple already went through this before with PowerPC -> x86

Not to mention 68K -> PowerPC.

Rhapsody supported x86, and I think during the PowerPC era Apple kept creating x86 builds of OS X just in case. This may have helped to keep things like byte order dependencies from creeping in.