Very interesting system. Overall I think it's an improvement. I have a few questions :
1. Will there be plans for canals and straits to be able to charge fees to trade routes passing through them? I feel like this would work well with the outlined system.
2. Will states with good harbours or locations get any kinds of advantage or bonuses?
3. As described, trade centers can only be built on coastal regions, a major benefit. Has any thought been given to also allowing this for states on major rivers and inland waterways? This would seem to me to make sense and be easy to add. EG for North America the whole Great lakes, St Lawrence River, and Mississipi should allow construction of trade centers. This could replace the MAPI bonus they currently get.
4. Will individual trade centers have any kinds of economies of scale separate from the national advantage described?
5. If treaty ports are now part of the original country's market, can you force the treaty ports trade centre to only trade with you? Can you levy your own tariffs on this treaty ports trade? What ways are there for you to gain revenue from the trade centres in treaty ports?