Obviously the bullet train is going to be a disaster, but if there were a high speed train (as in Europe) from SF to LA, I would definitely leave my car home and use the train. I'm only to happy to free up I5 for you.
I take the train from Santa Barbara to San Francisco from time to time and would even put up with a train with decent internet connectivity. Even if the train is slow, I could at least be doing some work on the ride. Unfortunately the train is currently more expensive, less productive, and slower than driving.
The technology to build faster trains was invented before man landed on the moon. It has been 49 years since this technology went into production. It's older than most people reading this discussion.