I'd like to see a simple mod where unit creation costs food. Every turn a unit is being built costs the city 1 food. Whether it be settler or tank unit. Remember, it's not just the hardware that is being built, but the training to use it. And a unit is not just a band of soldiers, but a larger group of support staff as well.
This drain on food should be separate from the total food absorption that comes with building a settler. It should happen first, then the total remaining food reallocation. And in several cases, this will cause food supplies to dwindle. In some cases, this would cause a city to drop in population. Totally understandable, without resorting to thinking of starvation. After all, a unit is the soldiers, and the people who support them. The extra effort of training mobile, independent groups stressing a community. Birth rates go down, mortality rates go up. It's all a part of the system. The game just makes no room for this.