What I really want are keychain cases, for either a single cart or double, that slide and lock in the same way you insert a game into your ds. I know that it's possible, because I have a case for my camera's cards that works in exactly the same fashion. It's a hard thin piece of plastic, with a slot into which you can push and lock your game into, and to remove it, you push again. These things NEVER fall out. And it's easier to retrieve your game - just push. And I want it on my keychain, because a keychain is easily accessible and I never lose my keys. And it would be easy as hell to flip through them. And very portable, very easy to move around. The only way it would get unwieldly is if you had like 20 games. I can imagine up to 15 being just fine on a keychain.
I don't anicipate having too many games. I am not made of money.