You know if you wanted to make a play off other great projects of interest in the world today, you could go with the theme or building colonies in space. On the moon or Mars... You can make it just in the near future.

Have all the same city bulding concepts, just base it off minerals and resources that would exist in that enviroment. You could make the game also follow the path of us all moving out beyond the solar system. Terraforming planets eventually, etc...