Let the rumor mills start flowing: in the recent 4.0.0 firmware update of the Nintendo Switch, Nintendo has added GameCube controller functionality via the Wii U’s USB-based GameCube adapter. In order to sync your GameCube controller, you must press the L and R buttons on the controller settings page of your Switch. It appears that the Switch can use the GameCube pad as a general controller — not tied to specific software — although the configuration is naturally lacking a few buttons.
While this update may be seemingly innocuous, this could have huge future implications for the Smash community, who have long wondered about the future of Smash at Nintendo. Could they be gearing up to release a port of Super Smash Bros. Melee, or Super Smash Bros. for Wii U onto the system? Or is it possible that we might be seeing an entirely new entry into the franchise? It is also possible that this support was added for use with other GameCube-era titles that may be coming to the Virtual Console in the future.
Source: Nintendo Everything