You know what’s funny? Nintendo put expansion slots on the bottom of all of their consoles prior to the Wii. In Japan, they were used for the Famicom Disk System, the Satellaview, the N64DD and the Gameboy Player. The latter was the only one that made it to the West. They never released an expansion for a console outside of Asia. They even had to retool several games that were released on Famicom diskettes for cartridges in the West, including inventing on-cartridge save files via battery-backed RAM for The Legend of Zelda in order to release them in the West.
Given Sega’s track record with console expansions, Nintendo might have been just as well off. Well, except for how the SNES optical drive add-on played out.