To fit in with the concept of Sea forts functioning as player bases or homestead, and to keep sea forts relevant It'd be cool if they could actually be utilized as a guild's base after clearing the fort (following the existing rules of phantoms respawning if no players are on the fort).
Once captured a fort could function as a "world event" with its own visual in the sky indicating the forts been claimed, guild reputation and whatever type of loot could be awarded on the basis of "x time occupied" e.g loot payout after occuoying the fort for 1 (in-game) day with a cap of 3-5 stacks of the multiplier. This could function as simply higher value loot dropping and increasing in quantity with each consecutive stack/"day" of occupation.
There could also be a multiplier on these rewards that increases per interval of time occupied (same time interval as payout e.g 1 in-game day). This multiplier isn't needed as much as t to increase or ensure player engagement/incentive in the activity.
If attacked by opposing players, the attackers, if victorious, should be payed out the equivalent of the highest reward tier the fort has achieved in reputation/loot drops. Keep in mind payout is as always in physical items that the player then must sell so any attackers could also have the benefit of selling loot that had been hoarded by the defeated pirates.
I think this would be a really fun and interesting way to further integrate the guild system into the game while keeping existing assets relevant. The main downside to this idea however is its counter to the concept of forts as a "short session" activity but with the introduction of the safer seas soon I don't see this change being too much of a loss as the safer seas accomadte a brief or more casual play style alot better.
Edit: as @b4njAx suggested the fort could be claimed by ringing the bell at the top of the fort, whenever Guild cosmetics such as flags or emblems are added, a guild flag or the like could be raised at the top of the fort which could claim ownership locking the treasury where the loot would spawn. On the sinking of the occupying guild's ship a treasury key could then spawn allowing anyone to unlock the treasury and claim the loot.
