A new Zelda or Mario game won't cut it, Nintendo needs a new IP. Zelda might have been big in the Wii and the N64 era but this is the Wii U we are talking about. A new Zelda game, even if it's the best game of all time will struggle to reach 2 Million copies. The same holds true for Mario, who did a measly 2 Million with Super Mario 3D World.
So what does Nintendo need to do? New IP's. Now the question is... what kind of new IP's? Western oriented IP's! They have to capture the western market by their big hairy balls and struggle them until they run out of juice.
They need to release something like "Mario in the Uncharted Islands of the Caribbean" or something like that. It should be in the same vein as Uncharted. A couple of shooting sequences (without too much blood). Some mediocre platforming elements and incredible cutscenes. We should have Rosalina and Peach as Mario's partner and they should wear tight jeans (perfect for mobility when you have to run from a helicopter that's chasing you down) and have their breast size increased to a "normal level" (normal for these kind of games being 90). They should also explore the "love triangle" that eventually develops between the 3 characters and have Mario choose one at the end.
Now Zelda... that's a tricky one. I think a "The Legend of Zelda: War God" would be a popular take on the Zelda franchise. A mature, dark, and goretastic Zelda game is all they need. Make Link grow some muscles (take out the femenine hair too... in fact they should make him bald). Make Zelda a big tits, almost naked, sexy woman and we are set! The story should have a strong theme in the vein of: "Self-pity for murdering thousands of people". And Zelda should be his guide throught journey. They could also include a sex minigame where link has an "implied sexual intercourse" with Zelda.
I am pretty sure there are a bunch of new IP's waiting around the corner. It's just a matter of Nintendo taking this chance. They need to show the world that they are still relevant and that they are willing to change to survive in this modern world.
Or they could just merge with Sony and be done with it. Or microsoft, or make me a CEO.
I'll leave an image here so you can ignore the wall of text I just wrote and be happy that I "didn't waste your time".
"I've Underestimated the Horse Power from Mario Kart 8, I'll Never Doubt the WiiU's Engine Again"