I'd like to see the entire city builder genre challenged by changing the perspective from city planner/god-mayor, to those whom they serve.
Imagine, instead of a birds eye view, you could only build from the perspective of a pedestrian.
Maybe in certain instances you'd have to see a wider swath of land for planning purposes (transit as an example), but it would be interesting to see how the forms of cities created by users change from this new perspective.