IMHO: I think they're probably always going to be different devices. VR will be the immersion device. AR will be very light weight and casual, for utility focused stuff like work, working out, maps, google search, pictures / video record.
AR gaming is going to be limited to augmenting things you can do in reality, like workout info, displaying speed when biking, etc. Pokemon GO search games. Board games. Mario Kart remote control car thing without the car. They could do some Astrobot / Little Big Planet stuff in the real world where he platforms around your furniture lol. Not sure what else. Football with the first down lines on the ground (but who would want to risk breaking it while playing football).