At the end of today's Nintendo E3 2019 Direct, the platform holder pulled an Apple and gave us one more thing.
It showed two characters riding a beast of burden within the depths of a dark crypt. Eventually, the pair was revealed as Link and Zelda in their Breath of the Wild incarnations! There's something brewing underneath Breath of the Wild's Hyrule, connected to an undead king shown in the trailer.
Those are all the details we were given in the trailer. There is a full Breath of the Wild sequel in development, but there was no release date, so we can expect to be waiting a while for that release. But at least it's coming.