To "devastate" freight service should get some award for dramatization. The line is about as near straight and flat as any railroad line in the US. For the sake of reliability, add a couple long sidings, lengthen the ones there, install higher speed turnouts at both ends of all sidings, and that should be enough. You do have several drawbridges, but the volume of shipping I don't know. Given the near flat profile, once a freight is up to speed, it will not be slowed by grades. Higher speeds into and out of sidings benefits everybody. You do have a gazillion road crossings, however particularly in the Bay St. Louis to Pascagoula area. However, once clear of the city, much of the Louisiana side is swamp without human habitation. The line does have several intermediate cities in Mississippi, so it would have a beads on a chain operation. My only question about the service is, given the relatively low population will the demand be sufficient?
The drawbridge problem could definitely affect reliability. Given that water traffic came before rail traffic, as a general rule water traffic has the right of way.
At one point there was a relocation study for this line. Having read it, it looked more like a response to some political pressure to look like "we are going to do something". Best I recall it moved the line to somewhere north of I-10 and created more problems than it solved. If they ever get serious about road crossing issues the most desirable relocation solution from my perspective would be to move the line about 25 feet, straight up. That makes right of way issues disappear. While we are at it, double tracking the thing would make most of the train interference issues disappear. Remember straight and level? If a freight once gets up to a 50 to 60 mph speed range it is able to stay there. Also, if doing this vertical shift, add some bumps in the profile at the various navigation channels to eliminate the need for drawbridges. If you question the practicality of this, look at the Escambia Bay bridge east of Pensacola. This was a low level timber bridge with a draw span. It was replaced with a multi-span concrete bridge with a profile enabling a fixed span over the designated navigation channel. The new clearance, I don't know, but I would suspect 50 feet or thereabouts.