I agree CA is way over-due....I think a 9.0 would definetly cause San Francisco to become an Island
The San Andreas is physically incapable of generating a mag 9.0 quake. Magnitude is a pretty basic function of the length and surface area of fault ruptured. SA is a strike-slip fault and simply not long enough to generate above a low 8.
The Cascadia subduction zone off Washington and Oregon and Northern California, is, however, capable of generating a 9.