If somebody wrote a plugin that simply moved the menubar (and the maximum top of fullscreen apps) $height_of_notch pixels lower and drew nothing but black above it, would you be happy? Because that would give you parity with existing macbooks.

No problem there. "Full" screen can just start below the notch. (Don't know if they'll do that, but they should.)

Think you misunderstood the parent comment. Full screen doesn't somehow add pixels into a bezel

Now you get the same amount of window space without losing the menu bar.

Full screen doesn't extend to the sides of the camera on current laptops. All that's there is the bezel.