I also think that the technologies will eventually merge, but due to current physical limitations in display technology I am not convinced that this is imminent. I'd guesstimate it at 15+ years. Adding and subtracting to incoming light, and doing it so that you can convincingly blend the two (allowing you to convincingly overpaint something that is bright in the real world with something that is dark in your virtual space while also allowing you to overpaint something that is dark in the real world with something that is bright in virtual space) is a difficult problem to solve. Probably some sort of hybrid LCD/AMOLED tech could do it.. but I haven't even heard of prototypes for this yet.