Nintendo originally planned to launch The Legend of Zelda: Breath of the Wild in 2015 (back when it was still just the ambiguous "Zelda U"), but it was first delayed to 2016, and then again until 2017. Many fans are expecting Breath of the Wild to launch alongside Nintendo Switch in March, but Nintendo has never officially committed to that. If the latest rumblings from the rumor mill are true, Zelda fans might have to wait just a little longer than expected.
On November 5th, industry insider Emily Rogers tweeted that Breath of the Wild might not be a launch title. Since then, she's followed up on this possibility with a blog post giving a little insight into the situation. According to Rogers, there have been rumblings since September that Breath of the Wild's localization process was proving to be "more work than anyone had anticipated." A source told her back in October that the process was still behind schedule, because Breath of the Wild is "A very ambitious game, maybe even too much."
Fast forward to November, and Rogers' sources have told her that localization probably won't be wrapping up until the end of the year. After that's finished, the game will need more testing, and due to its immense size, that could take four to six months. If this proves accurate, Breath of the Wild would miss the Nintendo Switch launch. Liam Robertson (best known for uncovering cancelled game projects for Unseen64) also says Breath of the Wild may not be a launch title based on his sources. Rogers speculates that it will likely end up as a Summer release instead, but Nintendo very rarely launches AAA titles in the Summer, so if it's not ready by Spring, it could potentially be pushed back for a Fall release.
Rogers also noted that she's heard Breath of the Wild will run more smoothly on Nintendo Switch than on Wii U, and that the final version of the game will be more difficult than the public demo that has been available thus far. As usual with rumors, none of this information is officially confirmed by Nintendo at this time, and we advise you to exercise some healthy skepticism.
Source: Emily Rogers