It won't happen in this console generation, and it probably won't happen in the next, but I'm guessing that by the time the Playstation 5 (or whatever) rolls around it won't have a disc slot at all. Game publishers have no interest in producing, transporting and selling a physical disc if they don't have to, and once consumers get used to the idea of downloading huge games to their hard drive they probably won't be that keen on having a physical disc either.