> The opposition would be insurmountable to making it take 12+ hours to travel from NYC to LA, for example.

It already takes 6 hours to fly. Add in security, checked bags, getting to and from the airport and it's close to 10 hours. Also you waste a day or ruin a night's sleep on the redeye.

Compared to that an overnight train with a bed sounds delightful. People could do almost-day-trips, coast-to-coast, with no ill effects. Leave LA tonight, shop/sightsee/eat all day in NYC, take in a show, hop on the late train back to LA the following day. This is pretty near impossible today unless you have a private jet.