A mod that would cancel orders to build cities after a certain amount of turns.

So, you can't build cities after turn 10 for example?

Sounds like it could pair well with stuff like, no attacking the first X turns

Yes, exactly. My 40 player diplo games usually last many turns, so eventually, the entire map is covered in cities, which inflates the income of the game and deflates the value of bonuses. I want players to think more strategically and long-term about where they choose to build cities.