Well, remember that SFO wants to restructure its runways. But there's no place for it to expand. Except into San Francisco Bay...

That's the plan being pursued currently, but any fill of the bay is an environmentally sensitive issue. New landfill is prohibited by law, and getting special permission to expand SFO into the bay is going to be a long, tedious process with lots of opposition. Don't expect resolution of this problem for many years.