-you should add islands where people can come raid and fight for the treasure, so liek they get an announcement saying an island had appear from the ocean etc etc, then people can go to the island and fight npcs or players in teams or solo to get the rewards from the treasure
-adding custom treasure trails where you get them from npcs, then i hope the server has lots of oceans
so people can travel to find the reward from the treasure map
-adding krakens as you sail, it will randomly appear to attack your ship, ofc youll need requirement to kill it
-under ground caves? to pick up loots that has been at the bottom of the ocean
-ghost npcs, or ghost ship that can allow appear in the fog