Much as I would like to see a resurrection of rail passenger service in Tennessee, most of these plans vary between being a dream and being a hallucination. Most of the routes are simply too slow due to alignments.
The most likely to carry any worthwhile number of passengers would be to extend the Chicago-Carbondale trains to Memphis. This would give a day train Memphis-Chicago, During ICRR days the daytime City of New Orleans would run up to 20 cars, with the loading north of Memphis being roughly twice of that south thereof. However, that was pre-interstate highways and an under 10 hour run time, and before Memphis became a high crime city where the general rule is "don't go inside I-240 at night", and best not at any time city.
Memphis-Nashville best time was around 5 hours and even pre-interstate the "good" day train was gone (in 1953) although the overnight mail train lasted into about 1967, carrying a single coach for the last few years. It parallels I-40 which carries a large traffic volume, but I-40 is part of a major transcontinental route because it is far enough south to dodge most of the northeastern toll roads and bad winter weather, so its traffic volume has not relevance to the rail traffic potential.
Chattanooga-Knoxville-Bristol with connections into the Virginia service. Sorry, again very slow alignment. Due to curves the highest speed allowed anywhere on the line was about 10 miles allowing 60 mph. Overall average run time speeds were about 35 mph. Major alignment work, or forget it.
Nashville-Chattanooga-Atlanta? Nashville-Chattanooga 150 miles by rail versus about 130 miles via I-24. Three hours was about the best ever time, and that was for the Georgian when the NC&StL was basically on this train owns the road mindset. Chattanooga-Atlanta around 135 miles by rail versus about 125 by road. In general the whole route is crossgrain to the Appalachian chain. Again, about 3 hours best ever time. The last 40 miles into Atlanta is a very curvy with a 40 mph speed limit. Again, major alignment work or forget it.