Maybe this is inconvenient for developers, but as a user, it feels awesome to know that the browser is technically capable of doing something, and does it when I ask, not at the behest or limitation of the PiP API. You know YouTube/Google would put this feature of my browser behind a Premium paywall.

So much of the modern web is "run your code on my computer," so this feels nice, where the browser is my tool to browse the web.