Is your feature request related to a problem? Please describe.
I was delighted to learn that the train system works perfectly underwater (messing around with the Origins Mod for infinite water breathing) except for the minor issue that none of the blocks are waterloggable. It's also difficult to mark depots and stations under the water as you don't see them easily on the map.

Describe the solution you'd like
Would you be willing to make some of the blocks (especially the Rail Nodes) Waterloggable?
Additionally, would it be possible to add a setting to the Dashboard to make it ignore water blocks on its map?

Additional Information
Ocean Monuments can make neat rail stations so long as you rebuild them away from the guardian spawns.
Sorry if my phrasing isn't the best.

Nice idea

Dashboard improvements will be covered by #818