Bullet trains would be good in tighter networks of cities. Southern Cal, Acela corridor.
But I'm just not sure the demand would be there for longer distances unless it's so cheap that it's worth the extra time.
Like what's China to Kunmung, a 6 hour flight vs a 12 hour train, at a comparable cost?
even SF to LA would have trouble with a high speed rail because the price would likely be the same as a flight
In Spain, a similar length high speed train route would be Madrid-Barcelona, that's 400miles and takes 2h 30min.
If you offer me the same price for flying than for taking the high speed train, I'll take the train every time.
In practice it'll take less travel time, no security lines or theater (no problem bringing your water bottle or whatever), you can bring more luggage, you can stand up/walk/visit the bar during the trip, you go from city center to city center so you don't have to spend an extra in taxis... I just arrive there 20-30 minutes before the train leaves and that's all.