The expansion port for the SNES was going to serve a purpose as a place to connect an add on called the Super NES or SNES CD-ROM add on. They actually made 200 prototypes called the [link|https://gigazine.net/gsc_news/en/20150706-snes-playstation/|Nintendo PlayStation], a combination of the SNES and PS1. The relationship between Nintendo and Sony had soon soured, so Nintendo went to partner with Philips, the creator of the CD-ROM format and the [link|https://en.wikipedia.org/wiki/CD-i|CD-i], a failed video game console. This didn't last too long, so 199 of the prototypes were scrapped. There is only one Nintendo PlayStation that exists in the world, which was sold at an auction for $300,000+ in February of 2020. There is however a [link|https://commons.wikimedia.org/wiki/File:Professor-SF-Attached.jpg|Floppy Disk extension] you can buy to run data on 3" floppies, but that goes inside the cartridge slot. Other than that, there is currently no purpose of that SNES expansion port. However, there is also a similar expansion port on the [link|https://en.wikipedia.org/wiki/Nintendo_Entertainment_System|NES] on the bottom that looks like a brick, and that also had plans for a modem, where you can play with people on your NES and on your [link|https://en.wikipedia.org/wiki/Sega_Genesis|Sega Genesis] called the [link|https://en.wikipedia.org/wiki/Teleplay_Modem|Teleplay Modem] designed by Keith Rupp and [link|https://en.wikipedia.org/wiki/Nolan_Bushnell|Nolan Bushnell] but other than that there wasn't a purpose to that either. The Nintendo 64 expansion port does serve a purpose for an add on called the [link|https://en.wikipedia.org/wiki/64DD|64DD] that was only released in Japan. This could play special designed Floppy Disks, and the GameCube had the [link|https://en.wikipedia.org/wiki/Game_Boy_Player|Gameboy Player] that both went on the bottom. Unless you can find the blueprints for the and CD-ROM add on or buy a 64DD which costs $1000+ depending on condition and games, there are no other purposes. Plus, you need a Japanese Nintendo 64 plus games in order to run the 64DD because the 64DD was only released in Japan.