Saying wouldn't it be nice without proposing how such a scheme would work without picking winners and losers is naive. The devil is in the details as they say.

Ubitiquious cross platform apps, sure! Just 3x your development team size - will your app still make sense to make with those costs? Oh don't worry - just replatform to a cross platform toolkit (and stop working on new features for 6-12months and retrain the entire team).

I just don't see why it's worth bringing the blunt hammer of government intervention here - let alone a reasonable path for regulation implementation.