This is decent advice on an individual level. Despite the fact that you probably can't sell your doomed house for a lot due to the current situation, planning a move is probably a good idea for those who can afford it.

But it's not really a solution on a population level. For one, if everyone sold their house because it'll soon be underwater, who'd they sell their house to? Aquaman? For two, a lot of people just won't be able to afford an expense like that. A large portion of the US lives paycheck to paycheck, and it's not easy to "just save up" a few hundred thousand when that means giving up on basic necessities.