alt Hacker Newsnerd-sniped me on this one. mainstream cool isn’t a thing. i think you mean successful. mainstream values success because it’s the vanilla proxy for a vanilla form of “value”.
so cool has always been about the “iykyk” kinda value. once too many people know there’s nothing to know anymore.
I think your cool only applies when you get quite granular. OTOH, everyone knows "teenager slang" is cool and "working in tech" is (now) cool, or "being a brain surgeon" is cool. So as I said in my original comment, those are two different "cool"s entirely.