According to rumors, Big N will soon be bolstering its gaming offerings for Switch Online subscribers with another console.
While Nintendo Switch Online offers a very small selection of games that many older consoles offer, it's not as extensive as its predecessor, Virtual Console, which was discontinued with the closure of Nintendo's Wii U and 3DS eShop. However, the big N offers more NES, SNES, Game Boy, Game Boy Color games, and at the most expensive level, SEGA Genesis, Game Boy Advance, Nintendo 64 or Mega Drive games, since they're not Nintendo consoles after all…)
A user on the Famiboards forum spotted possible references to a GameCube console in customs shipping data (you need to register to view it…), which could indicate that GameCube games may be coming to Nintendo Switch Online. The codenames and components are similar to previously released Nintendo Switch Online consoles, leading to further speculation. Another user supported the shipping numbers, but had reservations about their meaning. The inclusion of the codenames and parts could be a coincidence, as there is no reliable data yet.
Previously, Nintendo allowed support for older controllers on the Switch. Some controllers (like the NES controller) worked fine in games, but not all in-game features and functionality were supported. GameCube controller support could be a minor support feature for the upcoming Switch 2, though who knows what the truth is.
If Nintendo was really trying to capitalize on the Nintendo GameCube's lineup, it would be possible to choose from a lot of excellent titles, because although the platform wasn't very strong in terms of sales, there were some great works for it (for example, Eternal Darkness, Super Mario Sunshine, but also Pikmin started here), but we can only guess at this point. The Wii was built on the GameCube hardware at the time, so it might not be difficult to emulate the games.
But it's not official yet.