Seeing as how villages have been confirmed to be in I'm all for the job purposes. I'm thinking of that Millionaire Mod in Minecraft that did this so nicely, which might be the mod the OP is thinking of.
- You having to choose how to help them in exchange for a Civilization trade type menu. Access the list of what they can offer you for what you can then be offered in return. Doesn't have to be money. It can be anything. You can assist them with whatever they need and require for whatever you need in return. You help a friend move his furniture, you get food in return to feed yourself for a long while.
- Being able to request their assistance (or an AI Companion befriended from there; Possibly even through a mod addition) would be interesting. If you can get the option to befriend, or even have them companions for life (not love interest) then they should be able to follow, assist you, help build, lightly mine, farm, and etc. if you don't need them then you can escort them back to their village.
- Each villager should focus on their profession and similar. They should stick to their tasks at hand while asking you for stuff whenever necessary.
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I can now imagine railway networks, roads, and such linking player settlements to AI settlements and even merged ones. Would be an interesting mix and sights of things. Imagine shipping around supplies from one village to the next, more so on singleplayer for those that go deeper into role-play.