Going forward, Apple has a long experience with fat binaries for architecture 
  changes. 68k→PPC, PPC→IA32, IA32→x86-64. I don't think x86-64→ARM8 is anything 
  more than a small bump in the road.

Using the lipo[0] tool provided as part of the Apple Developer tools, it's pretty easy for any developer to create a x86/ARM fat binary. Many iOS developers have used this technique to create libraries that work on both the iOS simulator as well as a iOS device.

[0]: http://ss64.com/osx/lipo.html