These reports are unconfirmed, and there are no scans yet, but we hope you'll allow us a pre-emptive "whaaaaaaaaat?"
Why would the 3DS need a second analog stick/circle pad? The same reason the Wii needed a new version of the Classic Controller: Monster Hunter. The same sources report that an updated version of Monster Hunter Tri will be released this year, called Monster Hunter Tri G. The 3DS version is said to feature, at least, local wireless play. The existence of this game is also unconfirmed, but these two rumors kind of lend credence to one another. We'll let you know when/if we hear something official, at which point we'll probably be flabbergasted again.
Update: We've added a shot from Famitsu after the break. This thing is weird.