After the mid-1950's the major midwest to Florida traffic by rail was the City of Miami / South Wind duo. The every third day Dixie Flagler died somewhere in here. These were all two days one night to Miami. Their schedules, particularly the South Wind and Dixie Flagler were wound pretty tight. In fact, I think that is why the Flagler died first. It's schedule was nearly impossible unless everything went perfectly or there was major bending of the speed limits, possibly both. At the advent of Amtrak, only the City of Miami remained as a through train, and it was in decline due to the decline of the ICG.
The two nights and two days trains were still reliable up until their end, but their declining passenger loadings made that meaningless. In fact, by the early 60's all the through slepers were gone, You had late evening departures from several places, such as Chicago, Detroit, and Cleveland that got you into Cincinatti early morning, from which you took the Royal Palm to Jacksonville one day and one night to Jacksonville. Somewhere before 1960, the alternative Southland on the L&N dissapeared. The Southland had an advantage for those destined to West Coast (of Florida) points in that it did not go through Jacksonville. The day trains to Cincinatti and then on overnights to Altanta never did as well, mainly because it was evening again by the time you got to Jacksonville.
Since we can today do no better than the 1950ish trains, with much better roads today and the air service we have, there is little point in reintroducing Midwest to Florida service, much as I would like to see it.
It would probably be cheaper to upgrade track on some route between Chicago to Louisville so that the distance could again be done in about 6 hours and Montgomery to Waycross back to a 59 mph speed limit than it would be to do what it would take to be able to achieve the same run time via Atlanta, considering the amount of second main it would take for reliability and curve revisions or other line changes needed in the light that 6 inches superelevation is no longer practical with the high center of gravity of freight of today. Perhaps the best move would be to forget Louisville and do the upgrades on teh old C&EI-L&N between Chicago adn Nashville. Yes, this line is heavily freight trafficed, but it is fairly straight. We would be talking mainly about a lot of second main and additional or extended sidings, but the distance is shorter than via Louisville, about 450 miles via Evansville versus 490 miles via Louisville.
I often suspected that Amtrak added population of on-line cities to decide that the South Wind Route should be used instead of teh City of Miami route. They sohould have looked at which one had teh better ridership which was the City of Miami. However, evn that may not have made a difference. I think the main thing that killed it was the detriorating condition of all lines involved. If they had gone the City of Miami route, everything north of Russelville AL, where it went from trakage routes on the southern to ICG ownership was falling apart. For the South Wind route, that was everything north of Montgomery AL as that was either L&N or Penn Central.