The next update coming to the 3DS is going to allow downloadable content.
Nintendo President of America, Reggie Fils-Aime confirmed the ability to sell downloaded add-ons, but it clarifies that its up to developers if they want to use it at all. He states that they are simply creating the framework for the option to do so. He also goes on to reassure that Nintendo would make sure their own games are a complete experience.
Nintendo wants any DLC from themselves to be supplemental, rather than with held from the full game, which is great to hear from Nintendo, but I don't think 3DS owners are concerned about DLC. I'm pretty sure we just want any game to come out for it.
Source:
http://www.destructoid.com/nintendo-only-wants-dlc-for-complete-game-experiences-216050.phtml