That 4.0.0 system update for the Nintendo Switch is full of surprises. Certainly, Nintendo advertised it as adding video capture and allowing you to transfer user data to a new console, but they’ve kept a few features under their hats, including USB headset support and GameCube controller support.
You will need an adapter of course, but Nintendo and a number of third parties produced USB GameCube adapters during the Wii U’s lifespan to bring wider pad support to the console for Super Smash Bros. for Wii U.
This opens the door for more straightforward ports of GameCube games to a Switch Virtual Console, with the main distinction between the GameCube and Switch’s Joy-Con or Pro Controller being that the older console had analogue triggers, which a number of games will have used. At the very least, this just opens the door to using the original controller that the games played with.
It was reported at the start of this year that Nintendo were working on supporting GameCube titles via the Virtual Console, and this would be the first step on that path. In the meantime, however, it means you can do stuff like play Fire Emblem Warriors with a GameCube pad.