1. wuff! (HAZA!)
2. wuff? wuff?
3. WUFF!
4. Well, I think people are getting close. We were able to make DS/DSi games appear in the home menu, but they don't work yet. If you try opening it, you get that an error has occurred. If you try opening it with a DS game in your 3DS, it'll launch the cartridge rather than the desired game.
That's what inspired Apache Thunder's tool. It's the same concept, he just removed all the legal code, etc. If someone can find a way to redirect the code from wanting a cartridge to the SD, this can probably be possible.