That's wrong. The game key-cards are just a proof of ownership. You can sell the key-cards or buy used ones without any problem.
The only difference between a key-card and regular game cartridge is that key-cards will require you to download the game.
Nintendo is much better than their competition (Sony) in this aspect
People on this thread are talking about playing Super Mario 64 because they own their game. Nintendo has been ensuring you will not pass down your games to your children.
I'm also not arguing for intellectual property or copyright enforcement. I'm asking what comes next, I'm genuinely curious here.