Your simulation sounds incredible!
How big can cities get, though? One of the things I love about Cities Skylines is how massive the land plots are, and the tiny plots of SimCity 2013 was a bigger turnoff than anything else in its disastrous launch.
The real key will be to discover how to run a city simulation such that it doesn't all have to be "active" at the same time (e.g, the opposite of the Factorio simulation).
At this moment, not so big but lately I've done some interesting technical breakthroughs that will enable large maps :D ... or at least a lot larger than SimCity 2013