IGN - Zelda: Breath of the Wild was considered for NX release from the start, says Aonuma

Coming from an IGN interview with Shigeru Miyamoto and Eiji Aonuma...

Miyamoto

It’s complicated because as we’re developing this -- obviously development of NX started a while ago -- and unfortunately, I’m sorry, but the development of this game took a lot longer than expected. We really felt like we would be able to get it done last year, but there was a lot of struggle with using the physics engine, so that’s why it took a long time. Also, when we thought about developing a Zelda game for the NX, it would have to be way further down the life cycle of the system and this game, rather than really focusing on the unique features of the Wii U, it’s really a game you sit down and get into. There was a change in direction, so we decided to develop for both consoles a while ago.

Aonuma

From the beginning we were thinking of releasing this title on both platforms. With Twilight Princess, I was looking at, this [then-new] platform called Wii and I had more of an outsider objective view of, ‘Oh this is coming out'. But for this one I was slightly more involved with NX and just judging on the timing of development. When we were going to finish this, we thought it might be fun to have that available for NX as well. I don't see it as something too unfortunate. I think it's nice to have a single title that can be played on two different platforms. I should preface, I probably shouldn't say that because the staff working on this game. It's probably a lot of extra work for them so maybe they'll get mad. To them it might be an unfortunate circumstance”