To run multiple trains a day you need your own railroad. UP+BNSF can't allow it if they still want to run freight (which pays the bills, so that's the first priority of course). To make that separate railroad make sense, you have to spend money up front to allow it to run fast enough to do many multiple runs (hourly or better at peak times?) like a transit line, with minimum staffing (so the run has to take no more than a couple of hours to avoid significant service staffing needs). Since getting through the mountains is a problem, you probably will want to start up with a California end near a major freeway that goes to Vegas now, with plans to extend to a physically and financially feasible rail connection or corridor into the Basin when money and other stars align - that way you can siphon off some of the freeway traffic (a small effect on traffic and maybe building some word-of-mouth advertising) and get people generally to realize the option exists. Maybe even run some dedicated connecting buses from major points in the Basin to start with.

Does that sound more like Desert Xpress/XpressWest than X-Train?