On a recent Kotaku article, it was revealed that Nintendo do not sell the information inout into the app. This was in response to a question given to Nintendo, who stated “The goal of […] Miitomo questions is to spark fun conversations with your friends and for you to discover new facts about them as they answer the questions being posed. That’s why Miitomo generally avoids yes or no questions. As to the answer information our consumers provide through the Miitomo app, it is only used to provide a better experience for Nintendo consumers and to support the application. Neither Nintendo nor any of its partners sells or shares that answer information for any other purposes.”
While no one really questioned this until it was brought up by Kotaku, it is still nice to see Nintendo keeping user’s information private — to an extent, at least, for they still use it to market to you from within the app itself.