I've been brainstorming with me mates, and here are some of the ideas we have come up with, along with the motivations and effects on gameplay. We tried to think of content that would build on existing mechanics to keep true to the spirit of the game and avoid the whole "wide as the ocean, but deep as a puddle" problem.

One problem we sought to address is the frequency with which crews fight over nothing and end up feeling bitter about wasted time. I do rather enjoy the mind games and trying to read the value of a ship based on their actions. But I do think some tells, some subtle (like the whimper of the Chest of Sorrows or glow of a Villainous Skull), others obvious (like a raid cloud fading) would help observant players prioritize their prey.

Chests:

The Chest of Gales - The winds are rather fickle when near this chest. Shifting gales provide a challenge bringing it to port. A restless flag atop the mast will capture rivals' interest. The curse may become a boon, if to fleeing ye resort.

Sailing in general would be more difficult while holding a Chest of Gales. The shifting wind around a ship would provide a subtle tell to observant pirates looking for valuable cursed chests. However, a skilled sailor would observe a pursuing vessel's flag and turn against their wind to outrun. Therefore, nabbing a Chest of Gales would require careful planning to approach from upwind.

The Venomous Chest - If in golden serpentine figures ye delight, this treasure will allure. Grasping it robs of health and sight. Dropping it be the only cure.

The player has to be mindful of their health and thier step while carrying this chest. They may have to stop for a banana break. "Investing" bananas in a treasure is something seen in other parts of the game, such as feeding pigs or surviving a deep dive to a sunken ship.

The Cannon Chest - If this effigy of iron arms ye wish to abduct, be warned. For it be known to spontaneously erupt.

This chest would be built around a small cannon. It would go off at certain intervals, similar to the Chest of Sorrows. The trick would be to store it carefully so it doesn't blow a hole in your hull while you are exploring. Perhaps the ability to load it and fire it manually could add some interesting strategy, but I am unsure if that would upset game balance. It would probably add ambiguity to its function/curse.

The Kraken Chest - Jet black and oozing with ink, 'twill place a stain upon the ship. Those marred by the black spot are doomed to sink, when the beast arrives and tentacles whip.

The idea of this chest is to make the Kraken's appearance seem less random. By placing the chest on the ship, the ship would be stained with a black spot until destroyed. The black spot would increase the chance of a kraken encounter. The kraken could still attack all ships randomly, the two are not mutually exclusive. This just gives a crew the option to increase their chances of encounter.

The Radiant Chest - Adorn with a gilded sun, this chest can be hidden from no one. Piercing light will grant your rivals sight.

The purpose of this chest is solely to grab attention. Others will know you have treasure, so get ready for a fight.

The Heavy Chest - Only great effort will make it budge, and swimming it will stall. While on this slow and laborious trudge, shattered shins for those who fall.

Honestly, I am not sure I like this idea. The thought of adding something laborious to a game seems counter to the goal of entertainment. But it would provide an interesting dynamic, in that it would be hard to steal (Kind of like a less fun Chest of a Thousand Grogs).

The Chest of Storms - This treasure offers a personal umbra of gloom. Rain will flood, and sparks will strike. Act quick to dodge your doom.

Having a full blown storm form around the chest is probably out of the question. The consequences seem too far-reaching for game stability. Small localized rain clouds with lightning is more where this idea is going. Getting this chest to an outpost would require bailing water. It may also require fixing holes from lightning strikes, or the chest itself could actually act as a lightning rod, protecting you from strikes unless you are holding it.

The Ghost Chest - During the day 'tis out of sight. This treasure shuns the light. Ethereal glow envelops it, only during night.

This idea is playing with the attraction of attention. During the night, the chest is very visible. When in light, it becomes very faint and transparent.

Skulls

The Boastful/Vengeful Bounty Skull - A long dead captain tells his tale and leads ye down a treasure trail.

This idea is a proposal for a new but familiar feature that coincides with the Order of Souls lore. The Order seeks to gain the knowledge held in the skulls. What if some skulls are a little more outgoing with their knowledge? What if they can communicate to the player? The idea is that a Boastful Skull would lead the player to a treasure while a Vengeful Skull would lead the player to its rival crew.

How would the skull lead the player? Grab the bounty skull like normal, then press the button that you would to use any other object. Then there are a few options, the skull could present a vision (a map, a clue, or a landscape or island silhouette that the player may recognize) or a long, ghostly, snake-like tongue could come out of the skull's mouth and point in the direction it wants to lead the player. This doesn't change the core game, but presents the game goal/challenge differently.

The Infested Bounty Skull - A crustacean has made this loot its home. Lantern light may give it a fright so that it will no longer roam.

This skull has a hermit crab living in it. It will occasionally pop out and skitter around. It is therefore important to store it properly, so that it does not fall overboard. Perhaps light or attacks could scare it back into the skull.

I like the idea of light being used, as many players turn off lights to lay low. But if there are contrasting motivations for how lighting should be set, that provides more depth/importance to the choice.

Merchant Quests

The Missing Vessel - A shipment was expected from here to there, but it does not seem to be anywhere. Find the gulls and the shipment too. We don't really care what happened to the crew.

A merchant voyage could request that the player go recover a lost cargo from a sunken ship. The voyage would include the missing ship's itinerary, and the player would have to retrace the path to find the ship.

The only problem I could see arising is making sure the loot is there and has not already been plundered. But there is already a system for spawning skeletons seamlessly for Order of Souls voyages, so it may not be too big of a hurdle for adding some more interesting gameplay.

EDIT: Spelling