Just throwing out ideas.
Adaptations or possibly a new game - where the user has no choice but to cut down some forest or add oil rigs and refineries.
All to keep the same theme of course, educating through fun
on the subject of economics vs environment...
Saudi Arabia edition (with more irrigation challenges perhaps).
Political trade edition (with more transport/ownership/border challenges).
North Sea edition (with more transportation challenges).
I expect many of these things have been thought of but best concentrate on refining (pun intended) EnerCities BETA first though eh?
EXCELLENT GAME SO FAR!