In fact, the iOS Simulator used by developers today is pretty much just that, with the iOS app itself + the Cocoa Touch frameworks running within a OS X process

In fact, the iOS Simulator used by developers today is pretty much just that, with the iOS app itself + the Cocoa Touch frameworks running within a OS X process. The only difference is that simulator app builds are specially compiled for X86 instead of ARM (thus, it's not a "emulator" in the strictest sense of the word). With ARM, it'd be conceivably possible for the same iOS binary to run on both the device and the desktop simulator.