Nice pipe dream

I think I am safe in saying that the chances of the US having a high speed line like this are somewhere between slim and none, except perhaps in the NE Corridor or the west coast.
I remember an interview in TRAINS mag with Graham Claytor where he was head of Amtrak. He said that a very minor bump at 60 mph turns into a helluva jolt at 120. So as you pointed out, Bo, the track has to be impeccably maintained - read $$$$$$.
Even in our present day conditions, it is my understanding that all freight traffic is banned from the two center tracks of the NE Corridor because of the damage they do to the tracks. Claytor said that if a freight does - perchance - use one of the center tracks that Amtrak sometimes has to go out and do a realignment practically after each one passes. This means that as long as Amtrak has to share the same tracks - nationally - with the freight railroads there is little chance of our system being able to accomodate very high speed speed trains except in very limited circumstances.
In addition, typical axle loadings here are considerably higher than on the Continent, which exacerbates the problem.
The bottom line is that we probably won't be able to make the quantum leap, both technically and/or financially necessary to support 350 mph trains.
IMHO, the best we can hope for is to get our passenger service back to the conditions we had - say - in the 1930's.
CJ