Sure, if you can grow that subset to 100% then you can keep all the pizza for yourself, but the reason tech salaries are so high is the companies are that profitable.
If Zuckerberg is paying Alabama rates to everyone, it will be trivially easy to poach talent from him, and he knows this, so while he might have in mind a pool of "superfungibles" making $ALABAMA in $WHEREVER, you will not see Big Tech start slashing the compensation of the people they want to keep.
I already live in a low COL location and successfully demand Bay Area salary. So obviously I don't see a problem with this. Most people all across the country will see no appreciable change here. The only people who need to be concerned are people who are unable to demand a high salary based on their attributes other than geography.
The mistake is many people in the latter group think they are in the former.
Like many, I think I'm in the former group and will allow myself a little Schadenfreude if the latter group gets an "adjustment." Unless it turns out I'm wrong. :-O
There are many skills and levels of talent for which there is always a global shortage.
Who knows what will happen over some time if this really becomes big. Lots of people will leave the Bay Area and the cost of living will drop, in some places dramatically. Those 2m starter homes will get cut in half or more if this becomes wide scale.
Regardless, companies will still want to attract and recruit the best people they can and if that means having to hire from an expensive zone then they will. Or their competitors will and they'll be out competed. If anything though, over enough time if this becomes the norm than I'd expect places like the Bay Area to see the cost of living decline.
And then people will start moving in because CoL is suddenly cheaper and they get to enjoy all the nice stuff Bay Area offers without suffering through the daily commute...then CoL will rise again.
Then the top companies' headquarters will still be here, and there will still be a heavy premium placed on top of physical presence, especially for management/senior level employees, in fact I wouldn't be surprised to see the average income going up in areas like the Bay Area after the lower level rank and file employees move out.