Unlike a lot of people here, I think that a Utah-SoCal train would do quite well. Despite the reputation of the state, the casino's on the borders of Utah do quite well with Utahans and with the growth in the, what's it called, Wasatch Front, a train to Vegas would probably do fairly well, in addition to the travel between LA and Utah and Vegas.
Now whether this is worthy of investment over such a train that would or could serve, say, oh, lets say for arguments sake, St. Louis, Effingham, Terre Haute, Indy, Dayton, Columbus, etc is another question.
(note to/on the first paragraph, do well assuming good times, speed and reliability)