I'm picturing a game where you take the role of an arcology planner and are given a certain number of ingame years to prove the viability of the concept as fully as possible. Game takes place on an isometric grid, where you build your arcology out of predefined modules such as living quarters, industries, power plants, greenhouses, etc. You have to manage things like the flow of resources between districts, transit, waste management. You can connect your arcology to the wider world to do things like import resources and export waste, and you will need to do so especially in the early game, but you also gain a growing ability to handle these things within your arcology as you expand its capabilities. Maybe also have the player have to deal with structural soundness and making sure the arcology doesn't collapse. Scoring would probably be based on population, land footprint (smaller is better), and self-sufficiency.
Hmm. Maybe after Guardian Cry.
These are all good points. I have a few ideas.
Multiple different scoring criteria (e.g. population size, self sufficiency) that the player can prioritize - they can go for an overall good spread, or maximize any one, each of which should incentivize different city designs.
A "learn by doing" research system integrated into the city building itself. For example, recycling modules start out expensive and not really worth it, using a lot of power, processing very little waste, and recovering only a tiny fraction of resources. The more recycling modules you have operating, though, the faster improvements in handling waste are engineered.
Sunlight management. If all your residential and entertainment districts are in the center of the arcology, people will get sick of not seeing the sun and won't want to live there anymore. Sunlight would also be required for conventional farming (hydroponic modules would probably also be an option, but they would produce less food and require more power).
2d pixel art graphics. Not really a big hook by itself, but it would help it stand out visually.