Without going into all of my guesses as to why this hasn't happened in droves, I think one of the larger reasons is the access to cheap transportation back to those areas at night. BART stops too early, so for the younger crowd that likes to stay out, it's too expensive to constantly take a $40-60 ride out of SF. Without the advent of additionally public transportation, would it be economically viable to provide a paid shuttle service to and from SF / Berkeley / Oakland?