The brief mention of the Champion’s Ballad DLC for The Legend of Zelda: Breath of the Wild in today’s Nintendo Direct was not a detailing of the DLC itself, but rather the use of the Champion Amiibo within the game.
The four Champion Amiibo, based off the four long-dead Champions from the main game, will function much like every other Amiibo does within the game by generating items from the sky. The major way this set differs, however, is that each separate Champion will also drop pieces for a helmet based on that Champion’s Divine Beast.
Details of what those helmets do has not been revealed yet, but they definitely look cool. The Amiibo will be released on November 10, which is a good bet for the window for the Champion’s Ballad DLC.