And we will see whether Apple will allow such app in their store. I would imagine they will not, because they would rather have people using their own maps, but perhaps they will be benevolent this time.

Apple seems to have moved away from disallowing apps for "duplicate core functionality" - we have GVoice, Sparrow, Camera+ now. I don't see how they could not allow it.

If I had to guess, Google will attempt to get it into the App Store before iOS 6 is released. Apple will probably end up delaying approval of the app for a few months after iOS 6 to let users become accustomed to using their own solution.