Reading https://www.flightsfrom.com/LAX-JFK, https://www.flightsfrom.com/LAX-EWR and https://www.flightsfrom.com/LAX-BUF there are about 40 direct flights on that route every day. I guess that’s about 4,000-ish people.

That probably is not enough to make a train line profitable (they have larger capacity than airplanes, and you’d need fairly frequent service)

Luckily, as the crow flies, it is about 4,000 km from LA to NY, so a train route connecting population centers would probably be about 6,000. With a fast train (300+ km/hour top speed), the target of 30 hours will allow for some stops.

That will increase demand, with most passengers doing only part of the route.

People who'd like to go from NYC to Chicago in 10.

Denver to LA in 15.

I largely hate flying even though I've accepted it's the only way to travel overseas.

I'd love to take the full 30 hour train ride vs the 70 it takes now

People who can't spare 72 hours to travel on The Ghan ?

Long train journeys are a thing for some- with a private car there's also the appeal of views out the window while working on a script | program | report and having a car on a transport flat behind.

Not for everyone, but there are customers.

I have flown from Pensacola to Rochester, MN and it basically takes almost a day with plane changes, delays etc. 1000 miles distance. With a delayed flight it was 17 hours, I could almost have driven that distance by car in the same elapsed time.

With security and other hassles you basically burn a day in flight; so 30 hours NY/LA and being able to sleep, have high speed Internet, make normal phone calls, move around a bit, and eat (hopefully) normal food would not really cost any more time.