Personally, this is a deal breaker for me. I don't want to get paid less for doing the same amount of work. In a remote world, deciding where to live should be a personal decision of how one spends their income. Facebook doesn't pay employees less because they decided to drive an expensive car to work.
Facebook, along with all other tech companies, make crazy amounts of revenue per employee. The pay reductions will be a rounding error on the company's budget. Why not keep salaries the same and get the absolute best talent in every market across the world?