The only countries with city spacing on the scale of the US are the BRICs (Brazil, Russia, India, and China); (the long southern parts of Argentina and Chile are largely unoccupied). Brazil simply doesn't have a passenger rail network anymore (there's one line in one part of the country), which really only leaves China, India, and Russia. And India...definitely qualifies for this. Bombay-Calcutta is around 1200 miles. Shanghai-Beijing is about 1000 miles, and Guangzhou-Beijing (I'm using this as a proxy for Hong Kong) is around 1350 miles. And Russia is Russia.
Hmm, what about Canada and Australia? If Kazakhstan had major cities on the east and western end of the country, they could be 1500 miles apart.
Anyway, I agree with your previous post about the limits imposed by a once a day LD train network. With a intercity passenger train system that is skeletal at best outside of the Northeast, Midwest, California, NW corridors, impossible to schedule the trains to arrive and depart at all the major cities at convenient hours. Amtrak has to accommodate a limited number of connection options as best as they can.
When UP finishes the double tracking from LA to El Paso and the projects in CA, the westbound SL may end up arriving LA at 3:30 AM. What would happen if the westbound SL schedule were to be shifted to 2 hours later? Back to a longer layover in SAS for the TE, but the TE CHI-SAS schedule could be shifted with an hour later departure from CHI. Which, of course, impacts on the slot availability in CHI and the CHI-STL corridor schedules. With only 15 LD trains, there is a complex ripple effect on any change.