Wouldn’t it make more sense to make it so that runways can’t be built on water but instead there are terrain tools that’ll allow you to construct new land? Essentially it’s the same thing, but from a development perspective it make more sense to set the rules that way.
Different terrains are on the development list but no anywhere near the top so this would be something that we would look at once different terrains have been implemented. The environment and stuff like trees, bushes, grass, dirt patches and stuff like that will see an iteration before any release but it’s unsure wether water would make it to the initial stage.