Whomever wrote this needs to go look at job openings. I still see dozens and dozens that say "remote for now, then NY or SF". Until those companies decide that they can move or that people really can work remotely, SF and NY will be okay.
Why do you assume that companies will decide remote work is suboptimal and will go back to in-office work?
Because all the job describes say "remote for now" and I'm not willing to quit my current job in the hopes that they won't want me to move a family of 4 to NY or SF?
Except for the growing list of techy or popular firms that are all going WFH into 2021 or permanently?
The situation is definitely unstable. If elite workers manage to use working remotely to pocket the income taxes they'd pay, there could be a taxbase exodus. The governments of these cities could end up in a high-tax death spiral when this is added onto the bare costs of the CV disaster.