With the official reveal of Pokken Fighters Tournament, it seems to me like Nintendo could "Twilight Princess" Zelda U without really leaving a hole in their lineup.
Jan - Nada
Feb - Mario Party 10
Mar - Yoshi’s Wooly World
Apr - Fatal Frame V
May - Mario Maker
June - Splatoon
July - Xenoblade X
August - Kirby Rainbow Curse
September - Devil’s Third
October - Super Mario 3D All-Stars or Mario Galaxy 1/2 HD
November - Pokken Fighters Tournament w/Amiibo Toys
December - Star Fox U
2015 is fairly full as is, I did add a Mario Collection as an HD remaster, but I think that is really going to happen.
I also think a Mario Kart 8 Expansion could be coming in 2015 as well (ala New Super Luigi U for NSMBU).
So lets say Zelda U is pushed into spring 2016 ... I think this is right around the time Nintendo's next handheld (start of the Fusion line) will be.
If the handheld is powerful enough to handle Wii U engines ... well you can see where this is probably going. I can see a dual release happening, Zelda for Wii U + Nintendo Fusion handheld in spring 2016, just like what happened with Twilight Princess. Would probably boost sales of the game by an easy extra 1-2 million units.