Nintendo released a special adapter during its last console generation that allowed the company's favored GameCube controllers to work with the Wii U for Super Smash Bros. Melee and Brawl players who preferred that controller to continue using it in the latest Smash sequel (seriously, that's the only game the adapter worked with).  Now, unexpectedly and offered without official fanfare, we find out that the adapter works with the Nintendo Switch's latest firmware update and that it works for all games on the platform.  The console registers it as a wired USB controller.  Mike Williams at USgamer explains the caveats.

The Switch support for the GameCube controller extends to all games, you just have to make due without the ZL button. This means you'll be lacking features found in certain games, like Link's shield in The Legend of Zelda: Breath of the Wild. The fact that it works with every game actually makes it better than the original functionality on the Wii U, which only worked with certain titles.

I bought the adapter when it was released even though I didn't really need it.  I was happy using the Wii U GamePad to play Smash, but I had no idea if the adapter would be useful for other things later on and knowing how Nintendo underproduces items, I knew if I didn't buy at launch, I'd likely never have the opportunity again.  I have used the adapter more on my PC for emulation tinkering than I ever have in its official capacity.  Now that it works on the Switch, I suppose I'll play around with it just for the novelty factor unless there's a reason to use it over the stock Switch joy-cons.   If nothing else, it gives me a second controller for local multiplayer.

However, the bigger question here is why has Nintendo taken the time and effort to add this feature into the 4.0.0 firmware?  It's a quick jump to the conclusion that the functionality is there primarily for the assumed imminent announcement that Nintendo is giving Super Smash Bros. for Wii U a Switch deluxe edition release, and while I'd definitely buy that game all over again, if it turns out that it was added as a lark just to please a few customers, I'm fine with that too.