You are over thinking affordability. A 1 million dollar house is affordable to some people. It is not affordable to most people. A 100k house is affordable to many many people, but not to all. The problem is those who traditionally would be buying the majority of housing stock in the SD area are still unable to within prudence. There is no magic number of affordability for everyone. But if we are relying on bubble money sitters and the super rich, we are gonna be hurting.
So everyone who can afford with prudence buys, then what? It is only when supply of houses to the market and demand from people who can qualify and afford the payment are inline that affordability is met. Currently we have increaseing must sell inventory and reduced/constrained demand due to people not able to qualify for todays prices. Therefore prices are unaffordable in general and will fall. How far it falls is the whole reason for us being here.