I would love One giant city that I can have specialized sections. One area for mining, one for tourism, etc. --- I like to play blackjack. I'm not addicted to gambling. I'm addicted to sitting in a semi-circle.
I guessing if the city sizes were to 'increase' it would probably involved retweaking the current region geographical settings or add new region altogether. Anyway no here can answer your question directly we're not working for Maxis, go ask them in person if you're so dying to know. --- Even the most primitive society has an innate respect for the insane.