I think Nintendo's best strategy right now, and this is me being mostly an ignorant nobody, would be to gather a greater group of 2nd party teams. Monolith and Retro are excellent examples of companies that thrive under Nintendo's wing, and I personally would love to see Nintendo, for instance, invest a shit ton of money in Platinum, and directly reach out to indies to fund their development. In short, they need to become a little bit more like Sony in how they deal with small teams, and they need to become a lot more like a publisher in how they deal with their closest third parties.
I feel fairly confident they could turn this ship around with an actual marketing push (a real one), and exclusive partnerships with a stable of dedicated, well funded teams, they could make the Wii U *highly* relevant. And I say that as someone who actually knows the hardware, and how it seems almost designed to turn away multiplat games, but let exclusives sing.