Nintendo recently filed with the US Patent Office for a piece of technology that would allow 3D viewing capabilities for 2D displays without the use of glasses. The patent mentions using the device to track "the position and/or orientation of at least a part of a user". The patent also mentions the use of the device will give the player "collision-related game logic benefits".
This would be for things like jumping to avoid pits or ducking to dodge attacks. Another example was in game characters being aware when the player is looking away. The 3D would work similar to that of the Amazon Fire Phone, but using a different method. The device tracks the position of the users head, and updates the display accordingly (by showing slightly different images to the left and right eye) to present a 3D look in the same way the 3DS has the "sweet spot" for 3D on its screen. The device would create different movement speeds for objects in the foreground and background, creating a greater sense of depth.