They should do what they did with their SNES games back in the day: Put the special Nintendo seal on their products.
What I'm saying is, Nintendo should take the SD cards, and make it into it's own, Nintendo-only thing, that will only work on a Wii-and you could trade them. What's wrong with being able to trade with friends? You already do it with your $50 games. I think it would be cool to be able to trade VC games from an SD card.