The more there's uncontrolled violent crime, looting, riots and continued large protests obstructing daily functioning in large urban centers, that should help rush this process along. 

As to NYC, it's already happened, many of the major luxury purveyors have taken leases in Southhampton out on Long Island where their customers have already gone and are staying in their summer estates. Their kids will be enrolled in school there and when it's made sure they are the best available and that the police force has been enhanced, then they will probably be building a toll road into town so that all vehicles entering and leaving can be checked.

This, along with the lack of tourist taxes (always had huge taxes on hotels, parking, car service, airport fees and the like)  leaves NYC without much tax revenue to offer services to the poor classes left behind.

The upper middle class? They're leaving NYC too:

So keep rioting looting and demanding less policing, that will help chase all the money away.

Chicago should be a real hellhole soon. I imagine: garbage collection once a month...one fire station per a gazillion square miles...

Don't forget, the Obama's got themselves a little island joint to go to permanently, you have to take a ferry or a helicopter to get there