I think it'd be cool for some kind of co-op to be in Zelda Wii U. We've seen a taste of what it could be like with Battle Quest. I don't see the reason to not take advantage of the technology.
It's funny that you mention a co-op Zelda game because I've taken this into serious consideration as a way to introduce something new to the Zelda format (although not that only new thing). But I didn't want to limit it to some gimmicky technology debut (not to say Battle Quest looks gimmicky). So I literally wrote the development with Zelda as a playable option for a second player to tag along with. If no one is there to man the sticks, then a controller function allows the flip-flop between Link and Zelda. The dynamic team is a very integral part of the game design and so it offers a lot of potential.
As for the original post, my idea for co-op was actually inspired by the Tingle Tuner. It made playing Zelda that much more fun to play. I was the hardcore gamer and my friends, not so much, but we acted in unison to make the game more exciting. Anyway, I also managed to create two guide-like characters (one for Zelda and one for Link). Link's guide is a peregrine falcon that he can use to fly up high and patrol the surrounding area (as was mentioned), while Zelda's guide is essentially an information-getter. But given the WiiU technology it might be possible to recreate the fairy's purpose so that it can be operated with the WiiU Pad, using the Pad to steer and propel the little sucker to different targets (like the Beetle). Link's could also act in the same way, kind of like a self-guided hawk from TP.
Anyway, those are the two helpers. Far less annoying than past models, as it's the players option to rely on their help as opposed to their constant intervening (allowing for hardcore gamers to rough it, and casual gamers to have their hand held). I wouldn't get too into the capabilities beyond seeing what can't be seen immediately in front of you. Once you get too gimmicky it's hard to get serious with a game.
