I think there should be an oxygen tank that you can craft out of metal ingots, and also maybe reinforced flippers. These would allow you to stay underwater for much longer, the goal of which would be to go to a new area: the Deep Sea.
The Deep Sea could have new precious metals and resources used for crafting new, more powerful items that might be used for other things within the same update. I'm imagining an obviously dark underwater place (you'd need to be able to craft a headlamp as well) full of:
- Deep sea vents that damage you if you swim into them, but also have small white crabs (like the Hoff crab) near them that you can catch to cook up
- Anglerfish that bite you but drop glowing bio-luminescent 'pearls' if you kill them, these could be used to craft an upgraded headlamp
- Other creatures such as viperfish, isopods, giant tube worms, pelican eels, etc.
- Shipwrecks and/or sunken submarines, in which you could find lots of good resources
I'm just riffing with the thought that there should be something deep underwater, and I feel this could be a fun addition. Thoughts?