It should certainly be possible to put that in a MacBook Air to allow it to run iOS 7 and onward, so we can have both low power tablet and high power OSX in one small package.
There is no need to have an A7 in the Macbook Air to run iOS apps.
There is already a fully functional version of iOS 7 that runs on x86 based Macs and there has been since the app store was introduced. In fact I doubt that there is a single app in existence for iOS that hasn't at one point been run natively on an x86 based Mac.
When a developer runs an iOS app on the iPhone simulator for the Mac, they are not running on an emulator, the app is compiled as an x86 binary and linked against an x86 build of the iOS libraries.