They ran tons of a/b testing on user groups. I can tell you it feels fresh to me which is very necessary with aesthetics (fashion). Their main operating principle I believe is that they have acclimatized users to the position and flow of the UI for over a decade. At that point, you can embellish the UI.

If I skinned HN to anything you would still be totally intimate with where things are so long as I didn’t put yellow on light blue or something wild like that.