I would like to propose that trade system in Warhammer 2 be changed to one that's similar to Thrones of Britannia, where all connected factions would trade by default so long as they are not at war.
This would remove the unnecessary busywork of securing trade agreements and also be closer to the lore, where the various races continue to trade with each other unless they are hostile (traders from the Empire even trade with the Norscan tribes when not at war with them)
This could also be used to balance ports, whereby the Port has a smaller base income, but offers other benefits such as a substantial boost to income from trade, resources and industry (representing external and internal trade).
Additionally, I would like to suggest that the port building chain be integrated with the main city building chain. This would free up slots that the player could then use for other buildings.
The overall effect of these changes would be that Ports would be able to function as trading hubs and be valuable parts of the player's economy, while at the same time being more dynamic in their income generating potential. The combining of the port chain with the main settlement chain would allow these cities to remain valuable without the need to balance a separate building chain, whose base income would otherwise have to match the cost of upgrading and loss of a building slot.