I think Q4 2015 is when it will release

Nintendo is better prepared for HD development now I think. Plus, they've been working on it for a while now

If it's ready they'll release it.

If it's not, I don't think they will force the issue. They may even reposition it as a Wii U + Fusion launch title just like Twilight Princess if it slips to 2016.

They can slide Pokken Fighters in or move Splatoon and Xenoblade further into the fall if it can't make 2015.

There's no real crushing pressure on them with the Wii U anymore, it's going to go down as a relative failure with or without Zelda in terms of being a fair lock as their lowest selling franchise.

So they may as well make sure Zelda is the best game possible, there's no point in rushing it.

A non-Zelda 2015 I think would look probably like this:

Jan - Nada
Feb - Mario Party 10
Mar - Fatal Frame V
Apr - Yoshi's Wooly World
May - Mario Maker
June - Super Mario Galaxy Collection HD
July - Devil's Third
August - Kirby's Rainbow Curse
September - Xenoblade
October - Splatoon
November - Pokken Fighters Tournament
December - Star Fox U

I think they have it out by late 2015. They very nearly showed it in 2013 after all. Often the year we see a new Zelda in terms of gameplay footage, we see the actual game the year following.

Hasn't Aonuma vowed it'd be playable e3 2015?

They don`t have another system seller like Zelda, for next year.
A delay would leave the last quarter without a title to really sell the Wii U - against Halo 5 or Uncharted 4, for exemple.

The Wii U is not really competing against those platforms in a real sense (go ahead and try to convince a PS4/XB1 buyer at any store to buy a Wii U instead). 

Wii U is going to sell 17-20 million no matter what, the only thing that would change that is a miracle like Splatoon becoming a Pokemon/Minecraft sized break out hit or something, not like the next installment of a 30-year-old IP. 

Especially by the time late 2015 rolls around, Mario Kart 8, Smash, Mario 3D World, Hyrule Warriors, Bayo 2, Xenoblade, DKC, will all have come and gone ... really if you're not impressed enough by then to purchase a Wii U odds are you never were buying one anyway. Between Wind Waker HD, Hyrule Warriors, and Link/Zelda/etc. in Smash and Mario Kart plus Zelda themed amiibos ... most Zelda fans will already have the system (and most Zelda fans tend to like othr Nintendo IP too ... go figure). 

I think it's more important that EAD ensure this Zelda is really like GOTY type material and the best Zelda they can possibly make. If it's not ready for 2015, I'd just as well delay it to 2016. Even Wii U owners in the end will only remember how good the game was. 

TP and Skyward Sword weren't bad games, but they weren't "legendary" games either IMO, the next Zelda needs to be better, the next Zelda game should be to the Zelda series what Super Mario Galaxy was to the Mario series. 

Wii U will always be competing with the other consoles. Maybe not at the same level, but Nintendo will always try to convince as much people as they can to buy their games, be it Zelda, Smash, MK 8, etc. Those games can have an effect on HW sales.
And even if Wii U doesn`t surpass GC, games like Zelda are needed to make an impact.

GC "started" very well, but ended it`s life like so many Nintendo consoles: without support. Wii U seems to be doing the exact opposite: no real (consistant) support in it`s firt 2 years and now seems to be getting real support.
Of course, without 3rd parties, it will be hard to pull ahead of the GC.

System sellers will always have an effect for latecomers who only only later decide/want to buy a Wii U or can only buy a cheaper Wii U or really are expecting one of the big names to say: "ok, now it`s time to get one. I got all that i wanted".
WW is not a new game and HW is not a true Zelda game.

I`m not saying that the game shouldn`t be delayed even if there`s a good reason to do so.
But if you can`t get another holiday title of the same caliber, delaying Zelda will really hurt sales of the game and of Wii U aswell, in a time where Nintendo consoles usually do very well.

To be honest I think most "hardcore" Zelda fans already own a Wii U or will be the end of this holiday. Link in Smash + Mario Kart, Hyrule Warriors, Zelda WWHD, etc. 

GameCube finished weak but it didn't impact the success of the Wii at all, so I don't really see any huge pressure on Nintendo here. In fact that just goes to show that people have pretty short memories. 

Wii U is going to sell 17-20 million no matter what, doesn't make a huge difference if Zelda U is there for Nov. 2015 versus April 2016. 

Yes.
They said they could show something on 2013 e3, but didnt cos of wwhd.
They said wwhd helped a lot with Zelda u development.
These are evidences that they arent on the beggining of the development.

I think late november 2015 is a reasonable date.

To delay Zelda U to 2016 would be suicidal. The Wii U would be dead in the water.

It is INFINITELY more likely they would cut content than delay the game. The Zelda team has a long history of cutting content--especially dungeons--when their backs are up against a deadline, and they usually do a respectable job of making do with other content. If Aonuma really feels the content they're working on is critical to the game, he will insist they push it as a free download. Nintendo might push THAT in early 2016, but not the game itself.

I really don't think it will come to that, anyway. Cut content is what will happen.

Late 2016 could well be when the U's replacement premiers (or at least the 3DS successor which will be closely tied to the U's successor)