I have been thinking about the industry a lot:
It would be great if the ‘goods’ (which need to be differentiated for this idea i.e.: lumber, refined oil, steel and not “goods”) would be transported to industries as they are now, with the exception that the industry in the cities would actually use these and crank out commercial goods. these goods would then need to be delivered to commercial buildings (both in the same city and in other cities.) This should allow the player to make the ‘easy’ cash early on by simply getting a supply line into a city as is already done in vanilla, however provide the added goal of a more complex supply network that would have to take goods from one city to another and even could provide some reasons for supply lines within a single city (like a city courier.) I image this as 3 separate goods that are in demand uniquely in each city. there for, you could have one city producing one type of goods, but still have demand for another cities finished goods. This would require the differentiation of final products in each chain IE: refined oil becomes plastic goods (stealing this idea from cargo mod 😉 ), steel becomes metal goods, lumber becomes construction materials (or whatever)
Of course, the amount of commercial goods coming into a city to supply the commercial buildings will benefit the town and increase the value of commercial buildings and, in turn, raise the value of residential buildings based on the availability of high value commercial buildings.
Basically, industry in a city should actually act as industry and not just a repository for goods. why would finished goods go to industry anyways :p