The thing is, people used to try to do this with federal jobs in CA. They would work in CA for maybe 6 months to a year as a federal employee. Then they would transfer to a lower cost of living state (Arizona, Nevada, or Texas) and they would keep their same salary. Well the feds caught on and put a stop to that. So if you move, your salary changes too.
I am sure these tech companies are looking into that. Like yeah, stay home...move to another state, but don't think you are going to take your San Francisco/Silicon Valley salary to Dallas or Memphis. It might work in situations where it's just a couple people....but if you have a BUNCH of people doing it, they are going to make a change.