This is a really great idea! It's realistic and would make the world map much more complex and interesting!
I also want to be able to regulate the import and export of those cities/villages I control. It could be like: regulate which resource/gods the village are going to export, regulate the amount of imported and exported goods, and pricing the exported gods..
It would also be fun to make trade contracts with other kingdoms, or between lords, where the player can ask other lords for trade rights.
This would make trade become something that needs diplomatic skills and it makes good relations a lot more important.