Tunnels didn’t make it into the game but they are coming. CO explain how they will likely work.
The first content patch is currently in the works and one of the planned features for release in the update is tunnels. Nobody had any idea how these will function and look in the game but CO’s Marina has explained how they plan on implenting them in the update.
Creating a visual representation of movement in a tunnel would be incredibly hard so the method CO are suggesting makes perfect sense.