This is an example how it could look. [it is 2 x 1 supergrid dimensions] [FULL SIZE . 1 pixel = 5 x 5 tiles. here - http://i.imgur.com/w9HweMQ.png]


In summary, there would be large islands surrounded by sea. These island in the example picture would be the small islands. The bigger ones could be size of multiple supergrids.
Sea would play an important part in the game. Transporting personnel or goods , maybe whale hunting or large scale fishing.
Sea water wouldn't be drinkable, but you could gather salt - a new material.
This would require a new type of boat- a Sail boat.
Normal boat would lose most of it's speed in the sea, while the Sail boat would be fast in the sea, but slow in the fresh water.
Sea wouldn't be the only new thing. the whole geography would be more similar to real life. less river etc. Also grassland would not be spawned as default, but would only appear as you deforest the area.
Please share why you think this is cool or this sucks. thanks