I'm going to facepalm through the back of my skull if Microsoft go for a google glass type device rather than proper VR. Sadly it wouldn't surprise me one bit.
Well, all the rumors indicate that they are (see the Fortaleza leak). And I don't think it would be a mistake at all. The technology is currently evolving towards applications that work across different platforms, integrate into our everyday life.
Among the new features of the new consoles are multitasking, "pause and resume", second screens/remote play etc. It's all about using your device on the go, giving you the freedom to use different supports, in different conditions. And AR follows that trend, it's only the "third screen" that can be additional to the experience, but won't prevent you from doing other things.
"Proper VR" on the other hand is all about doing a single task with full immersion. You can't easily "pause and resume" a VR game (because you have to take your helmet on and off), you wouldn't do a video chat to see someone wearing a helmet, and running multiple applications would completely defeat the purpose of the technology.
Although they're having a lot of technical elements in common, I think AR and VR are completely different use cases. AR will more easily convince a large audience, while VR is more for the game nuts that would play on multiple screens or have a face tracking device on their PC.