Need way more things to craft. I know this game is in early production, and this suggestion is obvious, but there is going to have to be way more stuff to craft, meaning there needs to be more things to collect and harvest.
Would be cool if there were islands or structures (such as towers, abandoned rafts and ships) that you could come across while floating about, and then you could control your raft, with sails or anchor it (all new features, of course) and go explore. Here you could find maybe animals that you could hunt to have to fight, and some sort of enemies. Of course there would be loot but maybe its guarded sometimes by an animal or a dungeon even.
Exploring the actual water would be cool. Having to craft up a suit and gear and then go exploring the ocean.
More wildlife other than a shark. As mentioned, more animals that could be found on islands, or more fish in the water to catch. And when you go diving you can see all the fish and capture them with a net. Maybe you could even find an animal on a island and somehow bring it onto the raft, Noah's Ark style, and breed. This might be a stretch though.
Day and night cycle, with bed to sleep away the night.
And of course multiplayer, but seeing how the game is early in development, this might be a while before we expect this.
As you can see, I'm pretty enthusiastic about this game. I think it has great potential and I hope it never stops updating with new content. Hopefully these suggestions are taken into consideration.