The lack of usable hardware is the current problem now. I think Google Glass did it right, but was not liked by the average consumer as being overly nerdy. Other than that I think VR in a kind of glasses or a bain interface form would be an instant hit. Use cases range from e.g. police and military to everyday things. It would be amazing to e.g. take a look at a dark spot on the skin and get instant assessment if it is dangerous or building ikea wardrobe with instructions displayed over the materials....