Nintendo's software engineers brought their collective A-game when developing the 4.0 firmware upgrade for the company's Switch console, which introduced video capture support and the ability to transfer saved games and profiles from one Switch to another. If you already bought the GameCube adapter for Wii U, then you may already own a great controller solution for Switch. The only other peripheral you'll need is the GameCube controller USB adapter Nintendo released for use with Super Smash Bros. on the Wii U. It's still possible to pick up both the official and third-party versions of this USB adapter. This feature still does not work for Mario Kart 8 says the message switch on the news channel that functions as Mario Kart. The pad will be recognized as a wired USB pad. Just open up your controller pairing settings once the adaptor is plugged in and press L+R (the usual syncing combination) and off you go. After you've connected it, the GameCube controller will show as a USB controller on the Switch.
Getting the GameCube controller to work is easy. Who knows. The GameCube controller is a long-time favourite of serious Smash Bros players, which might hint that a new instalment of the fighting game series is on its way.
In the meantime, it seems that the hidden features in the Switch OS version 4.0 are more interesting than the flaunted features. You can play any Switch game with it, but you'll have to give up some controls (ZL is the shield in Zelda, for example), keep another controller on for the home button and get used to awkward mapping. It also makes it very hard to come back to the home screen menu on the Switch console but if you are really keen on going all retro, this should hardly pose a problem. Now that the controllers work, perhaps we'll finally see Virtual Console support on the Switch in the near future.