Read the FR notice (linked in the first post) one more time, and look at the RCTC documents noted in it. As Bob noted, some demand is undoubtedly there. This is a time for comments to FRA and other agencies scoping the environmental study for the overall corridor including any reasonable alternatives; specific project studies come later. And yes, it is acknowledged that there are constraints on use of the existing rail line.

The one thing I missed in the FR notice's recitation of other modes is bus. What bus service is there, and what could be improved, either as a train substitute or in combination with improved trains? I'm not convinced (Bob's comment notwithstanding) that the ridership is there to fill more than a few trains a day (if that many), at least at first. Spending a bunch of money on improving the rail line does kind of skew usage toward that, though, as a sunk cost (and it's not, of course, on the freeway, which is certainly a benefit in parts of the corridor).

Anyway, as said in many techy fora, RTFA before making many more comments. And for Observer: this is for the COACHELLA Valley (see: Palm Springs, Indio) not the CENTRAL Valley (e.g. Wasco and Corcoran).