In an interview with IGN, Shigeru Miyamoto has detailed some of the reasons why the game has seen such significant delayed. Obviously, the main reason for the delay was the eventual decision to release the game on both the Nintendo NX and the Wii U. The second, which we previously hadn’t heard was the physics engine.
“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.”
Eiji Aonuma, series producer spoke about bringing the game to the NX in the same interview.