Just a crazy idea here - since city size is already being worked on - has anyone given thought to a mod that would let you add new city zones to the blank spaces not being used in regions? Seems like an awful lot of wasted land on a few maps that could technically let you expand your region without hitting the city size issue.? =)
It's a shame they didn't just give us a true sandbox mode with a blank region, and the ability to just plop cities and regional road & rail.