Yea, especially with monocular VO, binocular has the ability to get some deph information, but it seems that the only valid approach are RGBD cameras like kinect (obviously too heavy for headmounting) and realsense. Im waiting eagerly for intel tango phones for that matter.
Well there is much less drift with SLAM with loop closure, and i’ve seen some applications of Large Scale SLAM with negigible drift. Here is an example Large-Scale Direct SLAM with Stereo Cameras (IROS '15) - YouTube.