Not sure how much of an impact a CD-based N64 would have had in the Western world, but it would have made a big difference in Japan, where it sold quite poorly and came third place behind the Saturn.

The CD-ROM format had become standard in the Japanese gaming market ever since the PC Engine in the late 80s, so it was only natural that Japanese audiences reacted even more negatively against the N64's cartridge format than Western audiences did.

Having a CD format would have given the N64 a lead over the Saturn in Japan, though this might have led to Sega exiting the hardware business even before they had a chance to create the Dreamcast.