It would be interesting if nations could declare war or trade embargo on other nations. Players would not be able to trade at ports controlled by enemy nations. Also, Kings or Governors could choose to allow or not allow pirates to trade at their port. It would keep merchants from pretending to be pirates and would give much more meaning to nation controlled ports. Any nation that allowed pirates would get more trade, although they might be looked down upon by other nations. A pirate owned port like Newland would become central, since realistically, Pirates can't just trade anywhere. There would need to be a limit on ports that each nation can have though, and a good system for Kings, Rules, and National Actions
So with the above as an explanation I disagree with Tilemaxos, it would need to be possible to kick players out if we ever hope to progress nations to engaging levels