There was the Famicom disk-system released in Japan which (I assume) used the lower port: https://en.wikipedia.org/wiki/Famicom_Disk_System - although that was based on floppy disks rather than CDs.
Not to be to nerdy about it but Famicom is the NES, not the SNES. The only thing released that used the bottom slot on the SNES is a Japan only satellite modem.