Amtrak is a flop and I doubt maglev would ever pay for itself either.
When you figure in the cost of federal subsidies, I don't think any airline has ever been profitable. And yet we need infrastructure. Why hold trains to a different standard than other forms of transportation?
It really comes down to how cheap you can make this. By my calculations, a trip from Washington DC to Philadelphia would take you about 40 minutes and leave you in the middle of a city.
To do the same thing by air would take you about two and a half hours if you check luggage, given that you basically have to be at the airport an hour ahead of time and it takes a while to get baggage and get from the airport to the middle of the city.
If it was less than $200 for a round-trip ticket, I would never fly that route. If it was less than $100 for a round-trip ticket, I would never drive that route. Now, if they make it so the trains had wireless internet connectivity and decent food, they could get really popular.