So long as there is transparency about how pay changes based on location, it is possible to do this fairly. The US Government civilian pay scale is a good example. If you are a GS-12 step 1, your base pay is $66,167, but that goes up with locality pay. A GS-12/1 in New York earns $88,651 but a GS-12/1 in Tucson earns $77,541. It seems like a big difference, but based on cost of living, the GS-12/1 in Tucson probably has a bigger house and fewer expenses. You could argue whether those numbers are right, but at least it's fully transparent. Companies that are moving towards this model should make transparency a priority. Perhaps you can negotiate for base pay and know that it will be adjusted by a certain percentage based on where you decide to live.
Much of this discussion focuses on how already existing companies handle the transition to remote work. This necessarily involves subjective perceptions of fairness.<p>But if you start a new company that's remote from day one, why on earth would you pay people based on location?