I would be hesitant of adding this because I have no idea how successful it would be, or if it would be able to fit in well enough, but I'm one of the many people (it seems) who would like to see a Zelda that shows an actual war in Hyrule. Whether it be a war we've heard of or some new one, it doesn't matter, but I don't want one for the story; I want one for strategy gameplay.
A war would be an opportunity to have the player direct troops in battle, either with a squad command system or with a more real-time strategy, over-head view system. With the Wii U Gamepad you could use both at the exact same time, with an map view on the touch screen that let's you move troops with your finger/stylus, and the buttons and sticks to control a soldier and give commands in the field.
I say this because I was a fan of the Battalion Wars games on GameCube and Wii, which merged third-person squad-based strategy with typical real-time strategy, and I think the Wii U would be the perfect home for its gameplay. Combining that with my desire to see a war in Hyrule is where this idea comes from. This is something I would be really excited to see in Zelda, even just as a one-off.