Back in 2010 siliconera posted information on a Nintendo patent, that showed some sort device that slots into the Nintendo DS game slot, here are some images:
siliconera didn’t post any source material to the patent at the time, but after a small while searching, i found the full patent filing here:
Cartridge for electronic game machine
Now you are probably wondering why i am talking about a Nintendo DS cartridge patent from a few years ago and wondering wtf it has got to do with the title of this article.
A French website called Nintendo-Master claims to have inside information and sources the above images as part of their claim, here is a very badly Google translated quote from the site:
According player Nintendo-Master, which has been confirmed by the information a famous video game publisher (which shall remain nameless but which develops the famous Final Fantasy), the parent company of Mario currently be working on a cartridge 3DS expected a bit special this year. Once inserted, it allows the portable 3D to communicate directly with the Nintendo Wii U making possible video streaming. Circle Pad Pro coupled with this cartridge allow the Nintendo 3DS to assume the role of a Wii U GamePad!