Some in-game options would be fantastic. Like, I can never actually hear the shark? I would think a shark angrily gnawing on a wooden structure while flailing around in the water would make a lot more noise :P So different sliders for game sounds, like ambient, music, player, creature, etc.
The ability to shift-click items between your inventory and the chests would be nice.
Please add a hitpoint display to the nets like the foundations have. Also, I feel like one plank should repair more than it does, considering that right now, it makes more sense to just build another one rather than repair.
I agree with a day/night cycle, that would be sweet. Weather too! Think about storms, blazing heat, etc.
More variety of fish you can catch, just adds some flavour (ha) to the game. Also, a greater variety of trees and crops. I'd love to see some citrus trees, like orange trees... or maybe lime trees, to play off the old 'limey' nickname. Some purely decorative plants would be nice too, maybe some tropical flowers. You could have a plant pot for them that looks like it's made out of half of the mini barrels that you see when you throw out an item.
And oh goodness, yes, furniture. Beds/hammocks, chairs and tables at the least. Maybe benches. Also, a need for sleep/rest. Doors? Thatch roofs?
Nets for fishing fish, maybe a system that means you actually have to have a balanced diet, or else you get sick?
More uses for scrap metal! I find myself throwing out a ton of scrap metal because I just don't have anything I can use it for. Maybe an ability to upgrade your wooden structures to be clad in scrap metal for extra durability against shark attacks.
An ability to throw the spear? I think this would make more sense than adding a bow and arrows, since, where are you going to get the feathers unless you add seagulls or other ocean birds.
Scenery stuff- like the occasional whale breaching the surface now and then. :) Rare pods of dolphins swimming by and jumping out of the water and playing. They could temporarily scare away the sharks.
Enemies- You could have crabs coming up onto your raft and pinching your toes, haha. Of course they'd be eatable once you stab them with your spear. Other foes too, like an ultra rare megaladon, an angry squid, etc.
I'm not sure how I feel about the island idea? I guess how you could do it, is have very small little islands go by rarely. You'd have to either hop off your raft if you're close enough, or risk the sharks if you have to swim a bit. There could be some rare resources laying on the island for you to pick up, probably mostly botanical. Then you have to race back to your raft and hop back on, again braving the sharks, before your raft gets too far away. Could add some excitement into the game.
Anyway, I just want to add that the development team is doing an amazing job, and I wanted to thank you all for such a great game. It has so much promise for a prototype! Keep up the great work!