Top GameCube titles could be offered on the Nintendo Switch through Virtual Console. Although the feature has not been confirmed, its existence was hinted at by Yoshiaki Koizumi, Nintendo’s deputy general manager.

We can not really answer with precision [about GameCube Virtual Console titles on Switch] because we have not announced anything about it at this time. What I can tell you is that we are working on things that go in that direction.
– Koizumi

There’s some possibility that old GameCube games could be remastered and released again for the console rather than being offered through Virtual Console. We won’t know until more information is provided by Nintendo.