According to Laura Kate Dale of Let’s Play Video Games, it seems that she has claimed that Breath of the Wild is indeed scheduled for a release in March in North America. Apparently finalized materials are starting to surface which is what Dale seems to have based her speculation on.
Dale’s speculation has also been backed up by Emily Rogers who was the one who previously indicated the game’s delay. According to her tweet, “You get some rumors right, some wrong. I expect to be right on Mother 3, Mario Kart. I expect to be wrong on Zelda. It’s coming March in NA”.
Of course since none of this can be verified, it’s hard to say if any of them are right in the first place, so naturally you should take it with a grain of salt and try not to get your hopes up just yet. Nintendo will be hosting a special Switch presentation on the 12th of January, so hopefully details about titles available at launch will be revealed then.