Nintendo has really boosted sales about all they can with their typical games. Smash might give it a boost as the franchise has never been on portables and has a passionate fanbase, but it's hard to see Mario Golf, Yoshi's Island, or Bravely Default really boosting sales.
If Nintendo is going to see a YOY growth of more than 3 million or so, they need something else. They'll either need a sub $100 model, and not a cheaper 2DS but something new entirely, a massive new casual IP, or a big hardcore IP like GTA or something. Other than that, I don't see the 3DS improving much.