I think the mistake right there is the fact that the Louisville to Florida AutoTrain started in Louisville and not Chicago! Chicago is probably the biggest chunk of the Midwest snowbird market (followed by Michigan & Ohio most likely), so an AutoTrain really oughtta start in the hub which also happens to be the most populous city in the Midwest.
According to that theory the Virginia - Florida Auto Train should have failed too. But it did not.
Lorton, VA is situated in the Washington D.C. Metro area which automatically places it in one of the more populated metro areas in the USA. Plus it's not too difficult to reach from other portions of the NEC either. Louisville, KY on the other hand is way more isolated and quite a distance from Chicago. If they ever attempt an Auto Train west of the NEC in the future, they should have the train in originate in Chicago. If you don't want to deal with downtown parking issues, then maybe set something up in Dyer, Indiana (Cardinal stop) so the parking situation is south of town like Lorton is south of D.C.
Louisville isn't dramatically farther from Chicago than Lorton is from New York. Service beginning at Louisville can draw from Chicago-Milwaukee-Minneapolis/St. Paul as well as St. Louis, Detroit, Cincinnati, Columbus, Cleveland, Indianapolis, etc. Service beginning near Chicago pretty much cuts off St. Louis, Cincinnati, Columbus, Cleveland, Indianapolis, etc.