If we focus to fishing entirely, then the latest market price changes encourage it. Tzogos for example, pays 13gc per crate right now. The party card gives 15gc. However the party card requires a significant investment in warehouse and there is also the card/turn cost which is involved. Plus, the party card requires more risky asset management.
Which also means that the extra income provided by the card is now very balanced. What we were discussing about the necessity to remove cards, is not any longer a key issue.
Theoretically, we can allow a food production port to purchase food. Practically, why would anyone choose to sell to a port for less?
As we see it, the proposed population consumption will further balance the trade system and populations across avonmora. The distance factor will also play a greater role. It already does but once population consumption comes, it will become even greater. At that point we will be able to introduce nation-driven prices on top of port prices (paying extra, to attract routes), which will be the national way of the Contract Shipping feature.
What I also wanted to say is that most probably, the final version of the population consumption feature, the produced resource, may not be consumed by the population. At least at the early version.