Take a look at the amount of 40 and 45 mph track on the Coast Route. It would take lots of Billions to make it 92 mph and it would still be lots of billions to make it 79. But the main problem is that the population along the central coast adds up to about one Bakersfield, certainly not a Fresno.
California Rail Schematics.
This is two years old but covers all conventional passenger rail routes in California. Informative.
Mind you I wouldn't mind a faster Coast Route, even if I would no longer be allowed to lounge on the rear platform and watch the world go by.