[RayChuang88]

In my humble opinion, high-speed rail--or to be more specific, trains that can cruise at speeds over over 220 km/h (136.7 mph)--makes the most sense in higher-density populated countries where you know there will be pretty strong ridership.

That's why it makes sense in Japan, South Korea, China, much of Europe, and certain corridors in the USA (e.g. the Northeast Corridor between Richmond, VA to Boston, MA). Interestingly, Chicago is one place where high-speed rail especially makes sense, since from Chicago these corridors work well for such lines:

Chicago-Milwaukee-Madison, WI-Eau Claire, WI-Minneapolis/St. Paul
Chicago-Davenport, IA-Des Moines-Omaha
Chicago-St. Louis-Kansas City, MO-Wichita
Chicago-Indianapolis-Cincinnati
Chicago-Grand Rapids, MI-Lansing, MI-Detroit
Chicago-South Bend, IN-Toledo-Cleveland-Buffalo

[hinckley buzzard]

That's why it makes sense in Japan, South Korea, China, much of Europe, and certain corridors in the USA (e.g. the Northeast Corridor between Richmond, VA to Boston, MA). Interestingly, Chicago is one place where high-speed rail especially makes sense

Well, it might "make sense" but it doesn't make cents, as there is only one profitable line in all the ones you propose, that is Tokyo-Osaka. Nowhere else in the world does highspeed rail support itself profitably.