"Although we felt that the development had been progressing well, we now believe that we will need a little more time..."
Shigeru Miyamoto made the announcement on Nintendo's Facebook page. He states it is perfectly reasonable to release the game this holiday season but it wouldn't be the polished product that we know it should be.
There have been a few games recently rushing their releases which have ended up costing them dearly (Arkham Knight on PC & Driveclub spring to mind!) so although frustrating to hear, it's the right decision.
His statement in full:
A Message from Mr. Miyamoto Regarding Star Fox Zero
I made a big decision last week.
We have been developing Star Fox Zero for Wii U with the aim of releasing it this year. Although we felt that the development had been progressing well, we now believe that we will need a little more time to work on areas such as the unprecedented discovery that we want players to experience in the game by using two screens, and further polishing the level designs and perfecting the tone of the cut scenes. While we have already reached the stage where it would be technically possible to release the title in time for the year-end holiday season, we want to polish the game a bit more so that players will be able to more smoothly grasp the new style of play that we are proposing.
To the people looking forward to the launch of the game this holiday season, I am very sorry.
Star Fox Zero is going to bring new game play and experiences that take it far beyond the framework established by Star Fox 64. All the members of the development team are doing our best so that the final product will not betray your expectations. And the game will not be delayed for a very long time – we’re aiming to launch the game in Q1 2016. Please stay tuned for further announcements.
Does this put you off Star Fox or is there enough on Wii U to keep you going? I mean, I'm going to say no...but I'm not the Nintendo fan boy. Steer me right Mario fans!