I don't know. I could be wrong, but I would think if any of the CA schools get passed up, it may end up being Pepperdine (unless Cal falls out of the top 16). Malibu isn't the cheapest/easiest place to get to. Hotels are expensive within 20-30 miles of Malibu.
Cal, Stanford, USC, UCLA will all be hosting women's regionals as well, and it may be better for NCAA to have as many dual gender sites as possible.
But if it's any of the other 4 that get passed up, I would agree that it probably would be Cal.