I'm going to apologize in advance for this. I'm a programmer by profession, so my immediate reaction to the MS Hololens was "this is a neat idea. I wonder how the public will mess it up?".
Honestly, if this takes off, I'm interested in what innovative and terrible malware there will be developed for it. My initial fear was making things that aren't there. People, monsters, cars, walls, bridges, etc. Then I thought "what about just changing things that are there?". Change an oncoming car to an oncoming squirrel, maybe move a chair 3 feet so the person sits on thin air, etc.
I'm only half kidding. I wonder if MS has something in it that can thwart stuff like that?