The killer for the restoration of the Gulf Coast is run time. Reality check, New Orleans to Jacksonville:
Highway: 546 miles, 8 hours of driving
Old Gulf Wind Schedule: 613 miles, 15 hours.
That run time goes back to when L&N-SAL were trying to run an as fast as practical train, not what would now be practical. I do not know what their maximum line speeds were, but in the 1960's L&N usually had a maximum 70 mph passenger train speed limit on signaled territory and 55 mph on unsignaled territory. SAL, I have no idea. The slight increase to the allowed limits of 79 mph / 59 mph would be relatively meaningless given other constraints.
Most of the extra 57 miles in distance is the dogleg Mobile - Flomaton AL - Pensacola. 104 miles by rail versus the direct I-10 highway distance of 58 miles. Then there is the unsignaled line Flomaton to Tallahassee, 248 miles of legal speed limit of 59 mph. By the way, signals with their potential 79 mph speed limit don't mean that suddenly you can run that speed throughout. You still have curves and other restrictions in play.
New Orleans to Mobile should be another story, as the road versus rail distance is about equal and the railroad is relatively straight (and flat). However, short to medium distance service need to have multiple trains per day to attract decent ridership.