I think that is a bit silly, why would you use the 3DS for the controls? If such device was made, I'd rather use the controls on the Wii-U controller because if you use the 3DS for the controls, you might as well play the Game on the 3DS.
I suppose they could do what they did with Pokémon Box where you could connect the GBA to the Gamecube and then you could play Ruby and Sapphire on the TV. Nintendo could make a App for 3DS games quite easily.