@coffeelight5545
I think your suggestion is a good one, at least directionally for the game. The devil is in the details of course, there are good ways and bad ways to encourage a bit of cooperation. As much as many might disagree, I think what you are asking for is actually lacking in the game, at least good implementations of it at least.
The game has always suffered from being paradoxically both cramped and sparse at the same time, and the game lacks any way to enjoy a bit of "friendly" competition.
Events are too small for multiple ships to partake without immediately resulting in cutthroat conflict. Yet, there is also so much ocean out there, it is sometimes hard to find players to cooperate with toward larger goals. Right now, cooperation exists when both players are rationale and realize that it is much more profitable to work together than to scrabble over chump change. But profit doesn't matter much to many players anymore, the economy is massively inflated and there nothing worthwhile to earn.
This is why I think you are right that cosmetics and challenges that encourage cooperation are an obvious unmet need in the game. And by challenges, I mean real challenge, not the forced cooperation that many are so fond of criticizing. It is only forced because it is "easy enough" to do it alone, there was no need to have other crews.
I think your suggestion is best accomplished in "instanced" areas through the portals. I am adamant these are coming to SoT with the way the adventures and migration tech has been evolving, but it is still totally speculative.
To be brief, I imagine them working like areas you can queue into on-demand, maybe with some kind of entry fee that could be gold, doubloons, or a combination of loot. You will be queued in with maybe one or two other crews. Some dungeons will be completely PvP enabled, others more limited / only allowed in certain areas, and others still maybe completely PvE in which the ships earn the same rewards for successful completion. Cosmetics would be an obvious reward, but I imagine these offering gold, trinkets for your ship, titles, and even small amounts of ancient coins / coupons to the emporium. To your point, there should be rewards worth the challenge, and this could be a natural way to introduce another sail variant with the V shape sails.
What you do in the dungeons to earn these rewards is a totally different conversation, but the main goal should really be challenging content with an element of "friendly" competition, and then maybe also with the option to enable PvP or allow ships to "invade" your dungeon for the chance of greater rewards. That would be the best of both worlds, and I think everything we are seeing is pointing to this. These could be tied into a larger community event or not, but the content is what really matters, to me at least. The story can be whatever it needs to be to support a fun and repeatable gameplay loop.