Never. If there's anything that browser developers hate, it's for their users to have fine control over what the sites they visit either save (or run) on their computers.

proof: they've had plenty of time, and even browsers that claim to be public services can't even keep the APIs stable for cookie/storage control.

opposing proof: Brave does.

I sure would love it if they came up with a way to block those "intent to leave" popups too.

Godspeed to Brave.