Maybe a DLC, but automated trading would be useful.
If I have a mega city, every year I could trade the same things in and out. The mega cities would have had a constant flow of resources coming in for money.
You could organise trade agreement, that could last for a few years or many years.
If you have a small settlement, you could automatically trade 2 or 3 cows at the end of the year before winter, and export excess food. It would add to the pressure, that you are committed to exporting. Also, you would get a severe punishment in reputation if you don’t meet your commitments.
If you had a settlement in a mountain area, you could export Stone, Iron etc and import a number of other things.
I just reach 2000 population, and had a large amount of excess cash and it would have made my life easier if I could have imported things.