Why/why not?

yes, nintendo needs it. simple as that really.

I don't think it will. I think they'll be nearly finished and decide that it needs more polish. As much as they need it, they also need it to be THE game that people need a Wii U for so can't afford to rush it out.

My guess is late 2016.

Pretty much this, Nintendo will do anything to get this out in 2015, even if that means ceasing production on another game and putting those resources into this.

Well, they also "needed" Pikmin 3 in the first half of 2013, but that didn't happen.

IF any big Nintendo game not outsourced to a third-party gets delayed appreciably, expect Zelda U to release in H1 2016.

Yes, because why not? They still have over a year to finish it.

Ideally Nintendo need it, but I can see Zelda and either Starfox or Xenoblade Chronicles X getting delayed. I'd prefer Starfox to get delayed.

Because they delay games on Wii U a lot. 

No because its the first Zelda as ambitious, big open world ans zverything, they tend to underestimate the développent time so i say 2016