Your description made think of the slime mold map of the Tokyo transportation system [1] albeit with a different set of inputs.
As with any organic, self propelled, system.. it matures and growth turns to maintenance, and eventually decay. Is the general argument here that SV has become a victim of it's massive organic growth, has it eaten up one of it's resources (housing, healthy diversity, etc) to the point where another city/system can now flourish??