I recently attended a meeting intended to help advise the new incoming mayor of San Jose about environmental initiatives he could take. The group was trying to limit the recommendations to a small number of items. At the end of the meeting, I tossed out as a last comment that the next General Plan revision should deal with the large land areas south of the city, near Almaden Reservoir and elsewhere. Those areas had been annexed during the foolish, expansionist years of the 1960s and 1970s but are not candidates for real incorporation into the city. City staff attending the meeting agreed, suggesting those places be rezoned from a residential to open-space designation (not exactly what I had in mind, but still a vast improvement). General agreement around the room, and the idea made it onto the list.
I think there's a good chance that this will go forward and eliminate some future developer's effort to put suburbs on hillsides. Something starting with a last-minute suggestion.