World event or voyage idea

I was doing a Legend of the Vail the other day and a thought occurred to me, wouldn't it be cool if there was a reverse to it? what I mean by this is an opportunity for you to take control of a fort and then defend it against a fleet of ghost ships. This could be waves of ships coming from all directions and if one makes it to the dock ghost could perhaps board the fort and attack you on foot adding to the chaos. There could be many waves and a boss (perhaps a ship larger than a galleon) that then drops a large collection of loot. My thoughts for the loot was it to be order of the souls loot maybe even with a new skull similar to the gold horde's chest of ancient tribute.