Working prototypes trump all theory.
I heard all silicon valley gurus stating they were "bearish on VR, bullish on "AR". This proliferated as a mantra throughout the industry. I thought they were wrong then, and believed the opposite - because I had a working VR headset that was awesome, but had only heard somewhat meh things about existing AR prototypes.
Until great AR hardware comes out, I'm still sticking with the same opinion.
Though there has been some progress since then.
Leave aside the issues associated with tracking objects in the real world in order to know how to virtually modify and interact with them. Leave aside, too, the issues associated with tracking, processing, and rendering fast enough so that virtual objects stay glued in place relative to the real world. Forget about the fact that you can’t light and shadow virtual objects correctly unless you know the location and orientation of every real light source and object that affects the scene, which can’t be fully derived from head-mounted sensors. Pay no attention to the challenges of having a wide enough AR field of view so that it doesn’t seem like you’re looking through a porthole, of having a wide enough brightness range so that virtual images look right both at the beach and in a coal mine, of antialiasing virtual edges into the real world, and of doing all of the above with a hardware package that’s stylish enough to wear in public, ergonomic enough to wear all the time, and capable of running all day without a recharge. No, ignore all that, because it’s at least possible to imagine how they’d be solved, however challenging the engineering might be.
Fix all that, and the problem remains: how do you draw black?
This concern is technologically narrow-sighted. We already have VR headsets with forward cameras built in. If the real world image is a projection too, you can draw whatever you want, including black.