This is cool.. I was trying to figure out how to get macOS next/prev controls to trigger events in Safari but haven't had any luck. This seems like a cool API for doing that sort of thing (though, sadly, no Safari support)
Yeah, it's pretty cool. I discovered it after noticing that Youtube playlist in Firefox started reacting on the player controls in KDE notification area.
And with KDE Connect, the Youtube videos automatically pause then you get a call and resume immediately after the call ended.