Got few ideas, not all of them will be exacly about on sea life but most of them.
Will start with ships, right now the patch says that after monday ships gonna be up to 50% cheaper and also we got that 2x resource bonus (which was not necessary outside of fiber realy as everything needs insane amounts of fiber). What want to suggest is reverse to making ships cheaper, make them much more expensive but make them last longer than 1-2 salvos. Right now all ships are just glass cannons, like 1 minute and one side is over. Medium planks right now have 2x less health than a frickin raft. Wish the ships actualy had a meaning other than suicide spamming them, don't want to build 5 schooners that die in 1 minute, want to build a schooner that survived even up to 10 minutes of bombardment, that's not like ships were sinking from few cannon balls irl, unless they hit the near bottom part of the ship. Basicaly what asking for is make planks have like 5x more health than now if not better. The battle that is won by steamroll in 1 minute is not fun, a battle that exhausted both sides and both struggled evenly matched that included many activities on the ship as reloading, transporting ammo, healing crew, extinguishing fires, boarding, constantly operating sails and the wheel and checking the captains skill of navigation, that would be much more interesting.
What's next that want to suggest to the above, different kinds of planks, a light wood plank that would make the ship lighter and faster but at the cost of plank health and negative armor (they would take more damage per hit), the other type of planks would be armored ones, very heavy, more health than normal planks and most importantly would have a positive armor (they would take less damage per hit), such ship with heavy planks also would move very slowly so for the price of being tanky, it would have o take any engagment thrown at it as a tradeoff and could be swarmed by tiny fast ships. Ships could be customized also to have multiple different planks, if someone plans to only fight from one side, they could have those armored planks on that side and normal/light ones on ever other side.
The other thing that would like to suggest that is now about on sea living is construction of platform, something like a mega raft, the platforms would have infinite weight capacity but they would not be able to build infinitely, a set cap size so no floating towers or islands. The construction would start in the middle of the sea. They by themselves would claim area arround themselves, however the claim would be barely going outside of the platform to prevent overlapping. The platforms would have alot of helth and maybe possibly even allow different kinds of platforms like with ship suggestion above? The platforms would not be able to build stone, that's too heavy to just make a town out of stone floating on the sea, walls and platforms could either be normal wooden, reinforced with iron or something. The platforms could maybe, just maybe be allowed to have sails?, so such mega rafts could after few real life days travel to another grid with good winds, imagine even having such thing crawling slowly on the horrizon as it gets nearer and nearer to the shore to bombard! There would be no "front" of the platform, the sails would push the platform in the direction they are rotated and the platform won't propably leave the shore for many many days, maybe weeks, considering shallow water slows ships down significantly. The platform would be allowed to build a special kind of small shipyard that allows building sloops insteed of rafts. Addition of this would enhance life on the sea, would create a new "land" to claim for newcomers, would add a new type of playstyle for players. The only problem that can see with this outside of struggles with surviving against whales/SoDs is technical problems as crossing the grids, how would it work?, would server be able to handle a fully developed platform pasing by without crashing?
Now something that is not about ships, venom arrows could be nice, killing poisonous creatures and coering arrows with the poison, crafting of them would be somewhere deeper in the archery tree, they would deal extra DoT damage, maybe some other debuffs as slowing target for the duration?, and also add the stun meter or torpor, whatever that is called like when snakes bite.
Please add tiny islands all arround with territory for up to like 3 flags max, they could work as an outposts or a territory for small companies or merchants, they would also add to the endless sea between those big clumps of rock and dirt.
Please make that traveling is more beneficial, right now islands almost have all resources on them and traveling only for like 1-2 different resources. Before the came went live, imagined self as a merchant of some rare resource aviaible on our island but right now, everyone can do just whatever on their main island without interacting with anyone else in trade.
EDIT: Also would like to suggest to devs a possible solution to ppl griefing by putting to much weight on ships or hoping on with too many ppl and sinking them, that's especialy for the PVE part as there is literaly no prevention to that as of right now. Remove the crew limit, make ppl actualy have weight, 60-70 kg per person maybe. And then make so weight doesn't sink ships anymore but just makes them stop in place. With this no one will ever be able to sink ships anymore, especialy that the sinking with metal tools was already patched.