Now this is a neat idea despite not giving a damn about Nintendogs. Slot-2 cheat devices dedicated to single games.
This idea is the first thing that came to mind after being disappointed in having beat Mario Kart DS in less than a single day. Ninetndo SO could have used slot-2 for track expansion packs to keep the game fresh longer but typical Ninendo they don't seem to ever go all the way and miss great opportunity's so often.