The interesting thing will be to see how remote work will change this over the next few decades.
If you’re being hired for a remote role then at most salary could vary according to time zone, perhaps a small difference due to taxation issues.
Paying 40% more to get the same value from someone living in SF has no possible justification (from a business pov) if you’re hiring for a global remote position (which is what Gitlab does)
If there’s actually a business reason someone living in SF might add more value they should hire locally.
This all sounds like a lame way of ratinalizing paying more to some employees who happen to live in SF (early hires likely) while pretending everyone is treated the same according to some equation.