I can certainly see companies wanting to pay less based on CoL simply to make the bottom line better. Given the way capitalism works, I'd say this is a near inevitability. The end result will probably be that the big tech companies are going to start "offshoring" work to the Midwest, and other low to very low cost of living areas. ("We'll pay you $70k per year, but you can live wherever you want in the US!")
I can't see this being good for employees, because there are significant benefits to living in a place like NYC or the Bay Area, and those benefits would be lost if people had to live in the middle of nowhere to make it worthwhile.