Make a new city-roleplay sort of mod that has no backdoors, very few bugs, makes sense, has many features, attempts to emulate real life as much as possible, cannot be abused, realistic, and efficient, as well as not taking up so many resources.
The ones we have right now don't come up to this level, which is why a better one would be great - including things like disease, sickness, the need to go to the bathroom, medicine, etc.
I bet if you do something like this, people could really see a difference. Oh, and make it public too - that will be a first.