I think it would be really cool to make a Virtual Villagers game where you build your village from scratch while doing quests. Think something like Bakery Story or Castle Story by TeamLava on the iPhone. I played BS back in the day and I believe they're still making updates for it. It's as old as the iPhone 3gs I think? You can actually customize your space, like constructing buildings or making recipes on appliances and serving food to customers.

The bad part about those games is the limited energy for actions or the need for real world money and high cost for everything and the missable items and events. Please please please don't do these things!
We need to have reasonable times for crafting stuff and completing quests. In those games, many people would struggle to complete events because their tasks would take ages to finish without spending money to instantly complete them! We also need to not drain our wallets while playing. Paying $9.99 just for extra outfits and furniture isn't fun at all. Nor is pay-to-win or pay-to-become-elite.

There's a ton of village/city building games that have similar DIY gameplay. But it would be amazing to see one that has that old-school, PC game Virtual Villagers touch! Games where there's not much player input are boring, IMO.

A Virtual Families expansion like Sims Freeplay only with less in app purchases would be nice. In that game you can renovate a whole town and have sims visit each others' houses. There's quests and furniture and stuff you can unlock from them, and tons of events. The devs come out with new furniture and outfits all the time and the game's been running for a long time.

Some type of exploration-quest game would be cool. I don't know, been nostalgic about Poptropica and I've been thinking about it a lot. Something similar to that would be fun. (OG Poptropica for the win!)

A mix of everything would be crazy. Crazy good!