There were rumours about this from a French website called 01.net, which accurately predicted the Wii U specs, or should we say leaked. This time they ended up hitting the mark again as Nintendo has announced a control extension for the 3DS.
– Peripheral places second analog pad towards the right of the ABXY buttons
– Attachment has an R2 button
– This means the 3DS will have L1, R1, and R2 buttons, but not L2
– Peripheral apparently clips onto the whole 3DS like a cradle (like a charger)
– Juts out 1cm at left, 2-3cm at right, 2cm at bottom, 2-3cm in thickness
This is what it looks like.
No other features are known, but Famitsu has labeled the expansion as “TBA”.
UPDATE: Twitter user south1996 also scanned a scan of the image of the 3DS with the expansion attached to it (below).