Speaking specifically about TP, the reason for the delay was pratically the same as the reason for Zelda U's delay.
Have no idea what was the reason given for other Zelda delays.
NX could be a handheld, a home console or even both.
Do i believe that something is launching next year? Yes, i do.
Do i see a big chance of the game being ported to NX? Given TP's case, yes i do.
Do i believe the game was delayed to fit this possible 2016 launch? Given the explanation, it could go either way. We don't really know what Aonuma was talking about.
Let's imagine NX really is a handheld and it's coming next year.
A port of Zelda U to launch the console would be a system seller, for sure. And seeing how Zelda delays seem to be for one year or worse, it's like everything falls in to place for a port of the game for NX.
Overall, what i wanted to say is that it already happened a Zelda game being delayed to make it even better and then seeing it also release on another system.