According to IncGamers, Maxis’s creative director Ocean Quigly has hinted towards larger city sizes in future updates to SimCity.
“That is just a performance decision. Given that was the performance constraint we decided to work under, we built a larger region environment and a bunch of the multiplay to work with 2km cities. At some point in the future, especially with mainstream computers become more capable, we could certainly make the city sizes larger.
We know that the size of cities will be especially small when the game is launched. It looks like Maxis are responding to player feedback and are at least considering expanding it in the future. Ocean finished the discussion with this bombshell:
“We’ll eventually get around to expanding the city size but I can’t make any promises as to when.”