That was there for a CD-ROM add-on, which was planned from the start but never actually released. Nintendo was working on it as a collaboration with both Phillips and Sony. After it got canned, both Phillips and Sony still had rights to some of the technology as part of the collaboration. So Phillips decided to release their own gaming system based upon what they had, and that was the (largely forgotten) CD-i system. And of course Sony did the exact same thing, and that became the Playstation. The rest is history.