The use-case I'm imagining for this has me seriously pumped - though I have zero reason to believe this will be a reality.
I'm thinking this will be a content consumption device, but also a work device.
Imagine sitting at a desk that has a mouse and keyboard, but no monitor. You put on your Apple headset, and an augmented version of MacOS is displayed infront of your eyes. The 'monitor(s)' you would use are projected by the device, while you still see the room you're in, and the desk you're sitting at.
This would allow you to have as many screens as you like, at whatever sizes you like, while arranging and manipulating them as you see fit (with a mouse, as we do now, or maybe with your hands). Alternatively, there may not be any 'screens' at all, but you simply move windows/apps around, or snap them to fixed locations; there are many possibilities.
Being able to see the world around you through the device would be key to this working - think AR, rather than VR. Information is projected into your world, as you can look down at your keybord for typing, or grab a pen and paper to jot down a note, or reach for your cup of coffee. I don't think a fully virtual world would be ideal for practical work.
With the way AR has been demonstrated in recent years, I don't think it's a stretch to think these virtual screens could be fixed to a certain position in the room - distance from you, as well as location relative to you as you move around.
Not only would this system allow for nearly infinite ways of organizing and displaying your work, but it would be familiar enough so as to not scare off regular people who aren't tech enthusiasts. Granted, there will be significant push-back from those who think they will look silly, but once they get over that, and look at this as being akin to sitting at your desk in front of three giant monitors, they can simply work within MacOS as they normally would - only with more freedom.
I don't think this is a novelty. I think this has the potential to revolutionise how we work day-to-day.