Another idea is add a net of canalization, it can produce wasted water.
Also you can add nuclear explosion, when nuclear station is burned.
Maybe new transport, like a trains, subways, trams.
More type of social buildings, parks, resting areas.
Possibility to adding helpers in townhalls, they can help you to react if city have problems(fire, crimes, etc.)
I can write many and many, but I now, that all this not easy to provide, so I thanks you for this wonderful game, and I wish you every success in your work!
