> Alternatively, in say 20 years or so, going to Miami which would take 21 hours (at 65-70 mph), could probably be done on an overnight sleeper-car (at probably something more like 120-130mph).
Believe it or not we already have this. It's an Amtrak train between DC and central Florida. You are a passenger aboard the train but your car comes with you! http://www.amtrak.com/auto-train
Let me guess, this costs quite a bit more than flying and renting a car for a week?
This is not a cheap stab at US rail, I looked into this on the similar service that the German railways offer - and it did not make financial sense over flight+rental.
Believe it or not we already have this. It's an Amtrak train between DC and central Florida. You are a passenger aboard the train but your car comes with you! http://www.amtrak.com/auto-train