I don't know how the Bay area will ultimately play out. I do know though that even given current building and whatever changes to policy that may allow for more housing and supporting transportation and other infrastructure in future decades, not everyone in tech can/should/will squeeze onto one small seismically-challenged peninsula.

There are physical limits for the short- to mid-term and there's some upper limit to what even wealthy tech companies are going to pay for new CS grads to work in Mountain View or Cupertino.