Since the beginning, Nintendo has been releasing products that kind of seemed like they could be a really good idea, but for one reason or the other they weren't able to fully follow through on the product by supporting it as time went on. I mean, I guess they each had a few games, but none of them ever ended up hitting it out of the park.
This list is in no particular order. Let's get started.
GameCube Modem Adapter
The really crazy thing about the GameCube Modem Adapter is that the system itself had a cutout in the underside of the machine called Serial Port 1 to fit the accessory yet (to my knowledge) it only supported one game online: Phantasy Star Online II. It was also used for local LAN between multiple GameCubes for Double Dash, Kirby Air Ride, and 1080º Avalanche.
Released in 2002, the e-Reader enabled you to use cards to unlock certain features in different Game Boy Advance games like NES Classics and a few others. Funny enough it was actually compatible with the GameCube's Game Boy Player accessory.
Back when it came out in 2008, you could get the Wii Speak accessory on its own or in a bundle with Animal Crossing City Folk. While researching this product, I learned there was actually a program you could download called Wii Speak Channel where you could have a chat room with as many friends as you want. Apparently there was no limit! I never ended up buying or trying this product because I couldn't see any of my friends using it either, so I think that's why the Wii Speak ultimately failed to gain traction.
I've actually never even seen a Virtual Boy in real life before, but it's fun looking at and thinking about this daring machine with a contemporary eye because it was like the first consumer grade virtual reality gaming system. Looking at products like Daydream View it's hard not to see the design inspiration from Nintendo's Virtual Boy that came out decades ago.
Game Boy Micro
This system was sooo cute. The screen was super bright, it had a high pixel density in comparison to the GBA SP and you could replace the faceplates. The GBM isn't on this list because it wasn't supported softwarewise, it's on the list because they just didn't make enough faceplate designs for it. You could buy a few extra ones at the launch, but I never saw additional faceplates after the initial run. Which is unfortunate, because it's a really amazing little Game Boy.