Today, Sabi, a known leaker with a good track record, revealed that The Legend of Zelda Breath Of The Wild 2 is currently scheduled for a 2020 release date worldwide. This isn't speculation, as he [sic] confirms that this is the current plan. He also added, however, that games in the series are often delayed, so there's the chance that Breath of the Wild 2 will as well.
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Not sure how accurate Sabi or Wccftech have been in the past, but a late 2020 release date for the game makes total sense, as Nintendo will presumably want a big game to be able to keep some of the spotlight on themselves in the midst of the PS5/Scarlet launches.