Aonuma confirms that work on the next Zelda has already begun. --@PushDustIn— Source Gaming (@AllSourceGaming) December 18, 2017
In the Master Works book for Zelda: Breath of the Wild, Eiji Aonuma confirms that the next entry is being worked on. This isn't a huge surprise obviously, as BOTW's development started after Skyward Sword's ended, but the direction of this new game will be interesting to follow.
For more interesting snippets, be sure to follow Source Gaming. They have a bunch of images and information posted on their Twitter feed!