Since the Photonic Engine uses Machine Learning and since its ML model would be dependant upon the camera/sensor, I doubt they would spend the money/developer effort to backport that to any other device that matched only on CPU requirements (e.g., an iPad that had the same CPU).
I know it can be frustrating/disappointing, but if it makes you feel any better, this happens with every generation (including features that seem much more trivial to backport.)