The ability to focus in VR using your own eyes requires a light field display - that is something which sends light rays from arbitrary angles into your eyes, and your eyes focus them.

Magic Leap has an augmented reality device that does that, although not launched yet.

My feeling is that light field displays will massively increase sense of reality - and reports of people using Magic Leap back that up.

However, I don't think it's necessary for lots of use of VR or AR.