Those came into my head yesterday while I was mapmaking, and I noted them down so I don't forget them again.
1. Rotate waters
This would be useful if you do a waterfall which isn't parallel to the map borders, or if you want a river floating down a hill.
The option to rotate waters exactly like the objects.
2. Collboxes
Some people might have already noticed that collboxes and collspheres don't move with the object when you rotate it in mapmaker. Which is an annoying thing sometimes.
So I was asking about changing it so that they turn with their object.
3. Shaped waters
More shapes of water planes than just the rectangle. Would be useful sometimes too.
4. Big waters
Remove the size limits of waters. Currently, when you make them bigger than 6000 they you can only swim in the water when you move inside the 6000x6000 square.
5. Ice
We had this option in IT.
To set a little extra script and the material didn't move anymore and you could walk on the water instead of swimming in it.
(Maybe an extra material for ice?)
-Thunderheart