According to The Wiire, it seems that "Super Mario Kart: Online" could be a possibility? In a recent interview about the Wii Shop Channel, it was revealed that Virtual Console games might sometimes have an "Update" button.
"The "Update" button indicates there are enhancements for the game. If you have already downloaded the game, you may select "Update" to download the enhancements free of charge. Please note, downloading the update may impact the saved game data."
Enhancements you say? Interesting, hopefully Nintendo pull their fingers out and get some of these old classics wired up and online. Other possible enhancements? New Tracks? New Characters? Mods for classic Nintendo games sounds somewhat like a dream come true.
We'll keep an eye on this story and let you know when we have any confirmed "enhancements".