Remember, take this with a grain of salt
Journalist Paul Gale, who currently runs his own website and has appeared in Nintendo Power in the past, has claimed that the sequel to The Legend of Zelda: Breath of the Wild is, or maybe was, at an earlier point in development, called The Legend of Zelda: Breath of Duality.
According to the intel, the sequel to BotW and its main hook is right in the name, which establishes on the “Breath” familiarity from the 2017 hit and giving a nod to the fact that you can play as more than the aforementioned title’s Link (including various, polar themes), hence “Duality”.
He has no direct proof to offer, though he is in a position that could allow him to be privy to such info. Time will tell if his report is accurate.