A trans-North America high speed rail route would be pretty cool. This seems analogous to the way sputnik ignited the space race.
Also, connecting 1.5 billion to 700 million is a lot more lucrative than connecting, what, 150 million to 50 million? Nevermind the fact that there are existing high-speed networks to connect with in Europe and China. What a fucking bummer it would be to take a 6 hour train trip from NY to LA then a 6 hour bus from LA to SF.
This is exactly the type of route that trains will not take from planes any time soon. The fastest train in the world is China's maglev that does almost 270mph.
But a trip from LA to SF, or St. Louis to Chicago, or NY to DC, or between any major city in Texas and any other one... that is the kind of route that rail would excel at, provided we had the motivation to build it.
All that said, I don't see the motivation to take a two day train trip from China to London when you could fly it in much less time. I understand the comfort factors and all, but when you are talking that length of time, I think the customer demand is going to be very limited (unless it's significantly cheaper than airfare).
In the meantime, read how GM paid to destroy our mass transit system so people would buy more cars.