I understand that it is unlikely to be added in such shot time before the full game release (and doubtfully needed at all), so I will disregard the specifics, but it will be interesting to see some economics (and maybe diplomacy) in the game.
It is possible to add some resources like Wood, Coal, Metal, Weapon parts, Explosives, Food, Goods and add the building tab with economic modules producing and processing these resources. Some will be to mine, some will require the area with a clear sky above to plant trees and produce wood. This is likely to require more area for cities in general.
Each city will have some Population and liable for military service part of Population, they will require food. When recrutting the crew, army-suitable part of Population will decrease.
When assembling the ship, you need the material like Wood, Steel, Weapon parts, Explosives. You get it from the stock in the current city or have it delivered from nearest cities with resource needed available. Or you can allow purchasing it from another fraction with Trade agreement.
It is possible to go even further and require specific weapon type to be prepared, but that could be too much.
Well, something along that.
Again, I understand how unlikely something like that to be implemented, but it does not hurt to dream, right?