I think both will *eventually* hit on the Wii U. Nintendo has to think that it owes at least that much to its core users. And from a business standpoint, Zelda could help move NX consoles, but the game also will not sell as well if its confined as a launch title. The Gamecube version of Twilight Princess, for example, easily outsold the Wii version.
Star Fox, however, was just delayed indefinitely into 2016. I still think that one will go gold faster than Zelda, but it's not far-fetched to think that the game may benefit from being a NX title versus just another Wii U game. Besides, it desperately needs a coat of next-gen paint anyways, and Platinum is the developer to do it, but I don't see any point for Nintendo to rush in getting it out.
It's not often said, but any industry follower knows the Wii U is an epic commercial failure and it's frankly too late to turn the tide at this point. Far better for Nintendo to just go on ahead and get these ready for the NX, too, so ports can be ready to go.