I remember that Nintendo was going to do a CD add-on similar to what Sega did with the Sega CD. First they were going to partner with Sony, then with Philips. Both deals fell through and there never was such a device. I guess the PlayStation was going to be a combined unit (similar to what NEC/Hudson did with the Turbo Duo which was basically a TurboGrafx-16 with the CD-ROM add-on combined in one unit.

I just know I looked forward to the SNES CD-ROM add-on more than I had any other system so it was a real disappointment when it was cancelled.