The thought occurs that a pop-per-city should be easily moddable if we create a local 2ndary resource that population buildings produce.
It might even work pretty good with the AI, because the AI only builds buildings it can produce so it will default to population buildings once it runs out of the local resource.
Edit: Nope it was pointless. the AI just goes "hurr... let's put some cheat multipliers on that shit!".