How about people living with multiple roommates, or renting out part of their house (I used to live in one of those situations)? Those people have a lower cost of living as well compared to others in the area.
Or does it only count if you're talking someone's sole and primary mortgage and where that's physically located? Even mortgages can vary wildly. In my city I can buy a condo for $100k or I could buy a mansion for 5 million dollars. My cost of living will vary drastically depending on what I decide to get.
The reality is that cost of living is really just a proxy in these conversations, really what we're talking about is the market wage for "premium" developers. I imagine over time remote developers will converge to a single market, but that it will take time, since there isn't as many opportunities for remote developers now there's not much pressure to move towards competing against remote offers. E.g., if I go to my employer and ask for a higher wage working remotely their likely response would be good luck getting a similar remote position. But as more remote opportunities open up you'll likely see more competition.
If there's enough remote positions and they're generally seen as equally desirable as in person positions we might even see everywhere going to a single market within national boundaries regardless of remote or in person, which would be quite interesting.
Or does it only count if you're talking someone's sole and primary mortgage and where that's physically located? Even mortgages can vary wildly. In my city I can buy a condo for $100k or I could buy a mansion for 5 million dollars. My cost of living will vary drastically depending on what I decide to get.