If Star Fox Zero is delayed, I honestly hope it's pushed all the way back to the holiday season (presumably after Zelda U's release), if not 2017 (or beyond / moving it to the NX) outright.
To me it looks like they're tried to milk too much mileage from a low-budget experimental project and --if the rumors are true-- it's now proven to take its toll on the gameplay. The dual perspective rendering of the game for both the GamePad and the TV seems to be way too resource-intensive for its own good, and whatever gameplay benefits it brings is outweighed by the game's presentation and performance.
They really should had saved it for another project (presumably, this was going to be used for the Miyamoto's remaining Project Giant Robot / Project Guard games) or lowered the scope of SFZ to a resource-light spinoff for the eShop; rather than a new retail entry. Especially considering how many other corners they've cut as it is: no multiplayer, compromised graphics, revisiting same locations --lol "it's not a sequel, but not a remake either"--, etc.
That said, I honestly wouldn't put it past Nintendo to pull another MT: Ultra Smash and AC: Amiibo Crossing and just bite the bullet so the game can make its April release date and give the Wii U something (other than Pokken and presumably #FE) for the Spring season. Regardless of whatever permanent damage it brings to an IP already on shaky ground as it is...