Ask HN: Instead of COL, should salary be a function of PPP?

Where PPP is purchasing power parity. I've seen lately discussion here about how COL is an underfitted model for adjusting salary based on location, mostly because certain goods (e.g. a Macbook) cost the same no matter where you are in the US (or whichever country your company is based, I guess it is more complicated if you are an international company). I wonder if PPP would be a better model for salary, and immediately it seems that there would be less disparity in salary between e.g. SF and a random rural town, because after accounting for rent and food, most other expenses are equal.

Finally I think a better question is, should salary even be adjusted within a single country?