It's something I've been hoping for a while now, and Nintendo have officially confirmed that Gamecube games are heading to NSO once the Switch launches.
Nintendo have announced that The Legend of Zelda: The Wind Waker, F-Zero GX, and Soul Calibur II will be launching first with other games such
The have N64 games on Nintendo online, which are still pretty Emulation resistant, so I assume they’re using a different method.