Listen, this would be ruining the tradition for LoZ, but either way this would be a great addition to the series.

Instead of having to watch your friends and take turns, you could both play at the same time!

Sure, the four swords is sorta like it, but not on a 3-D scale. Also with it would come online mode for LoZ. I personally love this idea (yet I don't have a clue how they'd do it...)