Eventually there will be an need for water to cure thirst to survive which means there will soon be lakes and rivers through out the map. This means that boats and submarines have a large potential to become a serious thing. Boats would be simple row boats that may be upgraded with barriers on the sides and roof to stop bullets but would remove visibility. Boats may be used for faster travel down rivers or getting access to larger fish in lakes. Submarines would be simple turtle submarines that would have upgrades such as larger air storage. Submarines would be used for more advanced raiding tactics and sabotaging people either fishing gathering water or just joy riding in boats. To nerf submarines they would be all self propelled and use up allot of food, they would also all be 1 man per submarine and would often have to rise for fresh air also if people log out in a submarine they will be sleeping by the nearest shore and the submarine would be up for grabs simply just floating on the water surface.
So boats, definitely, hopefully as they are developed swim speed is nerfed (there are already lakes and bays on the new maps) so that water becomes more strategic. By boats though originally I’m just thinking about rafts and this would probably be easiest and first to implement. Submarines like you describe, or essentially underwater air bubbles is an interesting idea. I can see it happening to some extent though I wonder just how useful they’d be generally.
Boats’d be sweet, submarines are a unique idea but I have trouble seeing implentation/functionality. On the topic of boats, barges’d be cool too, make a house for yourself off the coast or even make a group community barge town out on the water. With those it’d be difficult for people to take you down though since the viewable area would be so open, which I suppose is where submarines could come into play