The Secretaries: In SIMCITY 3000 the secretaries have their own personality and have a lot of say in their decisions, I think this is an interesting concept and one that ended up being lost over time, even in the most current games of the genre.
The Sims/People: In SIMCITY 3000, the sims themselves sent you proposals for laws, being very active as a community. This makes me think that in a city concept this makes the game much more realistic precisely because you know that in your city there are people with different opinions and they express them to promote changes in cities.
The Sims/People (2): Still talking about Sims, in SIMCITY4 they had greater integration with everyday life, for example, you could choose a sim to follow your day-to-day life, so he would talk about the problems in your neighborhood such as lack of policing or poor health, low level of education, etc.
Interaction between neighboring cities: I think there could be exchanges far beyond providing energy or water to your neighbor

Lot-based zoning system: I think this is not a new idea, but it would be interesting to better organize buildings such as farms, for example. Sometimes I zone an agricultural zone and it is disconnected because another farm soon appears next to it. This doesn't make much sense considering that farms generally have a large area of land with crops, etc.
Scenarios/ Story Mode: I think it would be interesting as an option for players, events like the Olympics, World Cup, etc. You would be in charge of preparing your city for these grandiose events.
Anyway, these are my ideas
