Lookup the Auto-Train from Virginia to Florida.
One route. Few departures. Only two stops.
They need more departures to increase convenience, Hybrid use trains like I suggested with less emphasis on passenger service per train could accomplish that more easily because adding a little capacity to numerable trains might be done at a lower cost than adding more dedicated trains.
The fact is that Americans are so oblivious to the possibility of going by train that we would need low risk baby step strategies at this point, which try to use what is still rolling and might build awareness of the option, grow the market if you will, not high risk grand schemes like HSR.