If you get the ideas of living in Manhattan out of your head, NYC is definitely more affordable than SF. So NYC does have the option of people just being able to move there.

The larger problem is how do the other cities compete at all in the future?

Smart cities are building out train based metro systems that connect their major universities and their airports to their downtown areas. (Houston for example). But that's REALLY expensive. It's not a coincidence that Houston, a city flooded with energy wealth, is one of the few cities pursuing such a strategy. They're one of the only cities that can afford it. What about everyone else? I think the other cities will need to get aggressive and creative about making themselves appeal to the bottom lines of tech companies.

If not, yeah, most will likely be left behind. Sad, but that's how the market works. Just ask Gary Indiana.