Raft is a good game with astounding potential, so I'd like to add a couple of ideas I'd like to see in the game. (This post may be a bit long)
1. Ocean expanse.
Raft has its own swimming mechanics which no player needs to use, since everything is done on the one immobile platform, so I was thinking that every so often, there would be another small raft that would appear on the horizon, which may contain chests, barrlels, lamps, and other things the player could benefit from. The player would then have to swim out and retrieve the loot before it floats away, adding a little more urgency as you have to temporarily abandon your own raft, leaving it vulnerable to sharks.
To hasten the trip between rafts, the player could also build small boats, allowing the player to go a bit faster and be less fatigued, however the shark can also attack boats, immobilizing the boat and forcing the player to deal with the shark or resume the journey boat-less.
Random Rafts could also be secured in place to form a permanent raft if they have an anchor attached, allowing for the player to see more random Rafts. This may however lead to the player creating a large bridge across the entire ocean, so the anchors will cost very heavily on rope and scrap, and each new raft that is secured might have its own shark.
2. Dangerous Depths.
So far, Raft hasn't been a particularly difficult game and is mostly grinding for more buildings, so the addition of new monsters and hazards would certainly get the blood pumping of the players. To stop players from creating enormous bridges across the map, foundation blocks would be affected by rot, which appears on a 1 in 500 chance, but only after a certain amount of things have been placed. Rot can appear on any foundation, regardless of whether it can be attacked by the shark, and will slowly degrade the foundation as time goes on. When it finally destroys the foundation, it will spread to each foundation and continue to degrade them. If a rotting foundation is repaired, the rot goes away and the foundation stays. This forces the player to constantly maintain and oversee their raft, or risk large portions of their raft being obliterated by long-term rot.
This next idea, while perhaps a little overkill, would be a very entertaining aspect if added. Every so often at dawn, the moon would appear red, indicating a blood moon. When a blood moon appears, two large red eyes will appear in a randomly determined water space near the player's raft. These red eyes of course belong to C'thulu, and if the raft near these red eyes is not well lit with torches and lights, then the raft that is near the space with the red eyes will be destroyed by a whirlpool. This will add the sense of desperation and hopelessness that a true raft should have.
At the cost of a little extra materials, the player would be able to reinforce their raft in key locations, adding a little extra durability to withstand the disasters of the ocean. Fortified raft foundations won't be completely made of metal due to the nature of rafts and can still be affected by rot, C'thulu and sharks, but they take longer to be broken.
3. Home Adrift.
This idea is fairly obvious, as it just gives ideas for more customization options in raft, but I figured I'd pitch it anyways.
They player would rarely be able to collects extra containers such as handbags, satchels and boxes which hold luxury items such as pot plants, bags, torches and other helpful items, along with small items to make you feel at home, like posters, playing cards and other trinkets and collectables. Luxury items help with practical purposes, while trinkets just help the place look cool.
That's all I could think of right now, I hope that you enjoy my ideas, and that they are not to difficult to implement into the game. Thanks for taking the time to read this, and have a good day!
-Omicron