Like the Elder Scrolls. And we could create our own items and give them particular effects. And create new locations and NPCs and program side quests. Maybe it would have to go through a vetting process so that no mod was ever game-breaking (eg no infinite durability 100-damage weapon in a chest in front of the Shrine of Resurrection). Then we could download them from the eShop. Maybe they could even cost money and have a similar structure to the app store (Nintendo get a cut). The game would last forever then, much like people are still playing Morrowind, Oblivion, and Skyrim today.