It appears that Nintendo has filed trademarks relating to the GameCube — mostly its fantastic controller — in the UK, as spotted by @Jo_ReggIt on Twitter and reported on by GoNintendo.
From what I’m able to gather, it doesn’t seem like anything NES/SNES Classic-esque is coming for the cube-shaped console, and all evidence it seems this is just a routine renewal for Nintendo’s legal department. However, I wouldn’t be surprised if this wasn’t in preparation of adding the console to Nintendo Switch Online, either.
It certainly wouldn’t be the first time (see the NES, SNES, and N64 controllers now sold by Nintendo for Switch Online subscribers, for example).