I understand your point. I think in this case, the author is talking about a scenario where the price of rent in San Francisco drops dramatically to where it is no more expensive than anywhere else relative to the opportunities.
At which point, even people who would find themselves priced out of SF in today's market would already have moved to the city if they wanted to.
At which point, even people who would find themselves priced out of SF in today's market would already have moved to the city if they wanted to.