It’s been confirmed, the new 3DS from Nintendo will be able to have downloadable content on it. This means that patches and additional content may be added to games. The DS in a way, was limited because of the lack of DLC add-ons, since it only had a Wi-Fi function.
Nintendo 3DS titles will be able to incorporate new stages, characters and a lot more after a game’s release thanks to the ability to connect to a specific marketplace (just like the Xbox LIVE Marketplace, PlayStation Network) But right now, no one knows how Nintendo will put a price on everything. I personally find the Wii Points/DSi Points system annoying.