We don’t really have anything like that planned atm. But there will be floating forts which you can capture, customize and move around the map. There will also be sea creatures such as sharks and big angler fish and stuff. You won’t really be able to tame them but we have something planned that might let you control some of them such as a shark for a short time. The idea we have is like some sort of escape spell that you can find that lets you turn into a sea creature for some time to quickly swim to shore if your ship is boarded or sunk, while also giving you the ability to use the shark as a weapon to attack other players that are in the water. Keep in mind though that these are still wild ideas and unproven concepts, they might not make it into the final version of the game, but they are certainly interesting concepts that we will experiment with. 
In other news, we have created a development blog where we will post updates very frequently. Most of the updates will be a bit more technical, but they will be very frequent. Have a look!