So this is definitely a long-term request, as I'm sure this is not a simple feature to add in. However, I would love for the ability to design my own cities in addition to procedurally generating cities.
I would love to be able to select which building type would go on which city block, what businesses are in each building, which apartments are available for the player to rent, etc. I would also love to be able to name the various buildings, cities, and streets.
I would love to build the layout for a city myself and be able to share it with friends eho play the game.