- Porting takes time and ressources. Games like Twilight Princess HD tooked around 2 years to port (they started anytime in 2014). Zelda wii u port will most likely be done by the zelda team themself (they wont outsource such a project, no way). So the time they are using now on Zelda port, they could put directly into the next zelda. Result: Zelda Wii U on NX will delay the next zelda for around 1 year (because they will "waste" their time with an port)
Porting from PowerPC to X86: http://www.destructoid.com/naughty-dog-porting-the-last-of-us-to-ps4-was-hell-275048.phtml
- If they port Zelda Wii U to NX and the NX will be a success, they will probl do the same to the next zelda. Any Nintendo console will be started with an new Zelda game. So the next Zelda game would also be on the NX successor (5-6 year development time = console cycle). This means the nx (in terms of zelda games) will probl be very useless.
- Most of us own a Wii U anyway. So getting the game on the wii u is not a problem. For those who dont own a wii u, it will probl make much more sense to get a wii u for zelda at NX launch. Even with an strong lineup, NX wouldnt had any chance to compete with the Wii U´s current lineup. Also the wii u will probl drop in priece when NX releases. Keep in mind, you have Smash, mario kart, mario 3D world, Mario Maker, Bayonetta 2, Pokken Tournament, Star Fox Zero, Xenoblade X, Splatoon and much more on the wii u. Even with a strong lineup, the NX could never compete against that. It will probl take around 2 years till the NX will have an as good game lineup as the wii u currently have.
So even if it would make sense for nintendo to port the game (more sales, better NX sales), it wouldnt make sense for us custormers/nintendo fans.
Thats why I think they should find other ways to sell Zelda on Wii U and to sell the NX (other new games, third party support).
BTW: Zelda Wii U on NX wouldnt even do AS MUCH. Skyward Sword sold just 3 mio copies on the wii, and that system already have an 100mio installed hw base. So do you really expects millions of gamers will go and buy the NX just to play the next Zelda? 97% of the Wii owners didnt even bought the last zelda, and they had the hardware to play it. The masses wont buy an NX to play an game thats also available on the wii u.
Zelda Wii U on NX will probl sell less consoles then Mario Kart 8 sold Wii Us.