sf is already a land of the rich... as of today it's rents are on par with NYC and house purchasing involves having 200k banked and another 250k annual income at the bare minimum.
so you missed the boat on stopping that one.
at the same time though, SF has one of the worst problems in caring for their homeless population ( to say nothing of the mentally ill and hopelessly addicted ) I've ever seen, and consequently huge crime. Now people living there will say otherwise, but at the same time they will also give you crap for complaining when your cars window gets busted in because it's your fault you left a back pack visible there.
the reality is, sf's problems aren't coming from better mass transit options. it's problems are coming from a failure to change in the face of a population boom. and i get that people want to protect the classical architecture of sf. and the skyline. and the environment. but the simple fact is, with demand as it is.. that means those houses will be worth millions. so either you get rid of SF's classical houses and replace them with larger condos and apt buildings, or you move to oakland / southbay. and i don't know if anyone has seen the development boom going on in southbay... but even with every hinderance the state of california and every lunatic in the bay area can throw at it, it's unlike anything I've ever seen. Mountain View in the two years I was there morphed into a completely different city, and every visit since I've left has been that much more startling. Where as SF doesn't change. between the classic architecture, and the city blight ( because they'd rather have a gaping hole in downtown for 20 years than approve a build plan that might offend someone ), what you have is one of the clearest contrasts between rich and poor in the entirety of he United States.
So basically... Google provided or SF / CA provided mass transit options aren't making SF less affordable. SF being unable to develop new housing options is. And no matter what happens the population of SF HAS changed. SF isn't what it was 16 years ago and never will be again. Same as how Mountain View is no longer farm land.
Accept that the SF you knew and loved 16 years ago is as dead as the Brooklyn I grew up in 16 years ago. We've both got to live with that. And if that means moving... so be it. Such is life. Things change. You gotta adapt. And that's something the bay area refuses to accept and that's the primary source of most peoples problems whether they want to accept it or not.