This may come as a surprise, but the NC line does very well (compared to other rail lines).
It would probably work better along the Boston, NY, Philly, DC line. A heavier concentration of the population along with a populace that is already somewhat accustomed to mass transit. Amtrak's best routes are in the Northeast, and I think that is where the first high speed lines should go.
Putting high speed rail anywhere in the South (except perhaps Florida) or Midwest would be a mistake imo.
There is one "high speed" rail line in the U.S., the Acela in the N.E. from DC to Boston. It is the only profitable rail line in the U.S.
The next best performing line (financially) is the North Carolina line. If it continues to grow at the rates it has been, it will be profitable in the near future.