What is a video game that you'd love to play, but no one has developed yet?

A God game/simulation game somewhere between Populous and Dwarf fortress where the behaviour is complex but the player doesn't have to do as much to keep things on the rails and the interactions are mostly just terrain manipulation and nudging. If you could build a rich, stable simulation that had simple rules, based on terrain, water, wind and weather and allowed the player to manipulate those things, i think it would be a really fun sandbox.

One of those 2D bridge builder games but the structures are in orbit, optionally patterned radially around an entire planet so you could build an orbital ring or other wacky megastructures.