Never mind whether a mirror is involved or not I still don't see any stills photographer wanting to hold a camera at arms' length while looking at an articulated LCD screen. It's just not the most stable way of taking a photograph. A viewfinder whether optical or electronic is essential. When shooting video a screen is more feasible as the camera is often on a tripod, shoulder rig or has some other means of stabilising rather than bracing it against the shooters eye socket.
