When do you think Virtual Reality (VR) will become the next big thing?

I myself think VR will be big in around 15-20 years. Once gaming gets to the point of near realistic graphics (hard to distinguish between reality and the game) then someone will want to go further and make virtual reality the best it possibly can be. What do you think?

P.S Yes I'm an sao fan and that is part of the reason why I'm wondering.