Atlanta to New York block time is somewhere between 17 and 19 hours. It is hard to do a reasonable daytime train with non-unfriendly end times. However, it is possible to do an Atlanta to Washington DC daytime train, and historically I believe that is what was done, when such existed. Or you could take something like 65/66/67 and extend it all the way to Atlanta. That would be fesible too, and possibly quite lucrative too.
Similarly Miami to Charlotte may be difficult, but Orlando to Charlotte may be possible, depending on how slow or fast Columbia to Charlotte is.
I am also dubious about the time tabling of a Palmetto style train between Atlanta and Chicago. Can Atlanta to Chicago be done in about 15 hours, like the Palmetto?
OTOH Chicago to Memphis would be eminently doable, even with plenty of daylight to spare in the summer.
Speaking of daytime trains, why do I seldom see mention of Chicago - Denver, which is actually doable?