One thing to keep in mind, for most of the trip, the sub will be surfaced and behave just like a power sailboat or schooner. The dives would be carefully scripted events (no crash dives, sorry) in shallow water (less than 100 feet) where there are no rigs, traffic, or potential obstructions (as well as can be determined).
The main concerns for surface travel would be traffic, unlighted rigs, and draft. That is not much different from the
thousands of power sailboats (coasters) who spend their time in the ICWW and Gulf here.
Far-fetched? Well, many thought a viable homebuilt submarine was far-fetched but Peter Madsen proved that wrong. That sub exists, works, and did not cost millions to build. It is not a military sub but it's very capable for transiting navigable waterways. There are issues over licensing, etc. But it is do-able.
Please fill out the survey. We need responses for the project
Neal