Hi, I got some suggestions. It might be a little difficult but I think it would be awesome.
So my suggestion is realistic water.
So when you grab a bucket from a small lake the lake will actually loose that water. Of course, if you take a bucket of water from a big ocean it wont really change anything. When you place the water in a hill it would flow down that hill.
If the water flow to a hole that hole would get filled a bit.
If you’ve played Starbound then you probably know what I mean.
It would be cool if the rain was realistic. So that when the rain hits land it would come water there. In a rain storm it would naturally come small rivers down the hills. Also, in rainy worlds you might wanna make your house on a mountain. (floods, another suggestion.)
Also, it would be awesome if there were waves in the ocean (and maybe even tsunamis in some worlds? :o).
I’m sorry if there are any typos. English is not my native language.