The demo they showed used the iPhone Continuity Camera, which has depth information and already does a great job of segmentation as it's required for the Portrait and Studio Light effects.
I suspect quality will be worse on a typical Mac FaceTime camera.
Good point, but not for details: I doubt that the depth information is of much help for separating hairs from the background.
You can always use your own removal with OBS. There's a plugin for automatic background removal and you can re-export the video as a virtual camera that any other app can use.