By principal I don't believe this for a second because I have subconsciously trained myself to never believe leaks until proven innocent, but I can certainly believe the possiblity of this happening. Zelda U has DEFINITELY got a ways to go, but because of the pressure Nintendo is currently under, I can see the Zelda team REALLY polishing up the early game to make it look really good for E3.
That, along with everything else we're seeing here could potentially make it pretty huge at E3; enough to make the many who don't own Wii U's really think about getting it after everything they see.
There is one very convincing piece of evidence that I believe debunks this rumor though: Mario Kart 8 at E3? Anyone who cares will have already had over a week with the game by then.