A piece of Group Content I feel is missing from BDO, is something that makes use of all the different skills we're building up on our characters... like... what's the point in the end of being a Master Alchemist or Guru Hunter, or Artisan Sailor if those skills don't affect endgame content, or don't make as much money as grinding in Elvia or other area's. Hence the idea for a Heist Dungeon, that would incorporate more than just Combat Gear, but also Lifeskill content as well, and be something that could be done solo, but would also be much better in a group. Here's the breakdown:

NPC Thresio Capon in Port Epheria will give you a Quest to destroy a Pirate Shipyard, with a set reward of ~30 mil silver... This quest would give the player a heading and location so they can take their ship(s) and Party Members to the Goldmont Pirate Fortress Instanced area to complete the quest, and start the Heist. However, once you cross Margoria and enter the Instance, you will not have access to the Central Market, or to Storage (Maids won't work here), which means you're only going to have whatever's in your inventories to complete the quest, and steal the loot from the fortress.

Approaching the Fortress, you'll find plenty of Goldmont Large Battleships trying to keep you from getting close to the island the Fortress and Shipyard is on. From here, the player(s) are free to decide how they proceed. You can destroy the Shipyard and leave, collecting the measly reward from Capon when you sail back to Epheria, or you can work together to start stealing loot from the Goldmont Pirates on the island.

Given the Goldmont Pirate ships will be respawning, someone is probably going to need to stay on their ship to keep any other ships brought in safe, and periodically check on them to make sure they're repaired... while keeping an eye on their own canonballs and rations, and keeping that topped up or switching positions with another player so they can restock themselves by grinding on the island, or producing food / repair items using loot from enemies, through gathering, or fishing as well as processing, or hunting birds.

Goldmont Battleships won't be the only threat either, there will be Pirates on the island that players will need to fight off, keeping them from damaging the ships, as well as clearing a path to all the different treasure chests scattered throughout the fortress. Pirates will drop standard trash loot, but will also drop assorted food items and Breezy Crystals that can be used to re-supply ships too, so Players looting the fortress can trade place with players protecting their ships.

The Treasure Chests count as trade goods, and can't simply be carried in inventory, they will behave as regular backpack goods that you'll need to bring back to your ship to store, meaning you won't be able to use your weapons while you're carrying them, and if the character takes too many hits from the Pirates, the trade item will be destroyed, so having someone clear a path will be needed for items deeper in the fortress. These items also wouldn't stack, so you'd be limited based on the number of slots your ship has to carry items, as well as applicable weight limits. Given these trade goods aren't part of the Quest, you'll have them even after you complete the quest in port Epheria... and given they're trade goods, their value will be increased if sold with relevant trade bonuses like the Valencia Desert Bonus... however, the Trade goods from the Goldmont Fortress would need to be appraised first before they're sold. Appraisals can be done with any Trade Manager, and this will set the trade goods Node of origin (Making Port Ratt the ideal spot to appraise and register them). 

While the Sea portion would keep a consistant difficulty, the Fortress and Island portions would gradually become more difficult over time, both with more pirates appearing, as well as with enemies becomming more powerful. This, combined with player fatigue and ship damage will eventually force players off the island if they haven't already filled their ships with treasure. There's every chance some party members may leave without any loot if they don't get a turn on the island before they need to leave, so co-ordination is key to making sure everyone gets rewards from the raid. Because the Heist items count as Trade goods, they'll be destroyed if the ship they're on is destroyed too, so PVP will also remain a factor once outside the Heist Instance. 

Bosses: There would be two Boss Enemies for this content, one being a Goldmont Pirate Flagship that has a random chance of appearing, dropping an RNG Lootbox with appropriate rewards (Perhaps even a chance of a Nol?) and a Goldmont Pirate Lord guarding the largest treasure room of the Fortress. Both Bosses will require multiple Characters to fight, but can be looted by the entire party regardless of weather or not they did damage, as other party members may be filling other necessary roles. 

As Thresio Capon's Quest is required in order to travel to the Fortress, it could be locked as a weekly quest fairly easily. Overall the above content would offer a unique Survival - Teamwork Gameplay that I feel BDO is missing and could benefit from, as well as offering a certain thrill if the loot value is high enough... and given it prettywell uses existing game mechanics for the most part, it should be fairly easy to implement, even if other similar dungeons don't get produced in this format.