PBS is showing an episode of History Detectives, and they are doing a story on a Civil War sub found near Lake Pontchartrain. It didn't have the most illustrious career, but the design was remarkably similar to the film version of the Nautilus in many ways.
So, always interested in taking Discovery Bay's Barbary Coast elements for DCA, but keeping the Verne elements for the Frontierland expansion, couldn't Disney take the 20K story, written just a few years after the Civil War, and use that to develop a broader backstory for Nemo, in which he learns the secrets of the New Orleans sub builders, takes his knowledge back to Vulcania (represented in the Frontierland expansion) and returns to wage war against the warmakers?
[Then too, the film of Mysterious Island features Civil War soldiers who arrive at Vulcania by balloon. Verne's Five Weeks in a Baloon could tie into this, as well as the Hyperion of Island at the Top of the World. You could play with the hot air balloon motif in a CircleVision film, and use it as a means of "travel" to Helluland for an exciting Viking ride...]