Nintendo will be releasing an update for the 3DS in December that will allows 3DS and Wii U owners to combine the two Nintendo eShop account balances. Nintendo announced the update during a Nintendo Direct earlier today.
3DS users can register their Wii U’s Nintendo Network ID, which enables them to join both eShop accounts. This allows them to buy Wii U titles using the 3DS’ account balance and vice versa. Should you not have a Wii U, however, you can still create a Nintendo Network ID.
Furthermore, with the new update, the 3DS will get Miiverse support for the first time ever. Now 3DS players can share tips and interact with other players around the world. Maybe point out where the Pokemon X/Y legendaries are or how to get a Sylveon in the shortest amount of time.
Additional information regarding the update cam be found here.