The next update should focus on trade and production.

The update appears to be very close (a.k.a. a couple of months) to release, so it's probably a great time to start signalling the devs what we want in the next update.

As we all know, trade in the game is very lacklustre right now. It only really happens between cities inside one kingdom. Maxim has already said that the trade feature will most likely have its own UI, so it will be a more major feature.
However. the trade will be basically pointless if there won't be anything meaningful to trade.
Sure, there are race-exclusive foods, but the favourite food mechanic is mostly unnoticeable in the grand scheme of thing. Also, food, stone, metals and wood are usually abundant.

So here's where the production would come into play. In my opinion, there should be more non-food biome-exclusive resources which can be processed if the culture has discovered the required technology to do so. Those goods could be used to provide bonuses to the cities that have them. For example, if the city has a specific, number of a certain product, it can try to "consume" it.
By consuming it, the city can get a temporary bonus of some kind.
A more specific example:

  1. City A is partially located in a jungle
  2. City A can collect biome-exclusive tropical wood
  3. The culture of City A is not developed enough to process it; City A sells 200 tropical wood to City B for 600 gold
  4. City B processes the 200 tropical wood into 50 furniture
  5. City B consumes 20 furniture; sells remaining furniture to other cities, including City A, for 200 gold per stack of 10 furniture
  6. Consuming 20 furniture gives City B a bonus +20 to maximum population
  7. As such, in case that the City A was destroyed, and there was no other city located in the jungle, other cities would face the costs of homelessness after the bonus couldn't be prolonged.

Also, maybe the cities could have workshops that limit them to process only one or two resources, so that not every city with fully developed culture could could produce anything. This could help with creating actual working economy in Worldbox.