Should the placement of a shaft below water be allowed? Seems that you can move a shaft to another part of nauvis-underground where above on the nauvis surface is water, and it will allow this, but once a player uses the shaft, they are stuck in water and can't move or do anything unless they have landfill.
Not sure if this should be the behavior or not. Putting landfill automatically would allow players to exploit moving the shaft around to create land bridges above. Perhaps not allowing placement if the surface is in water is a good strategy.

Also, placing from the surface to below ground without a cooldown of some sort on an already placed shaft seems op in the sense that they can carve out an area underground just by placing the shaft multiple times.