Ferries don't travel at 200 miles per hour. They also don't have the same limitations as trains, such as maximum widths and heights imposed by existing infrastructure. Train length and weight would be another one, given the requirement to haul a half dozen or more autoracks with every passenger railcar.
I like the idea, but the engineering and safety issues around it haven't been resolved yet, and doing so would only add to complexity, cost and time needed for the project.