Zelda Expansion Pass $20 DLC for both the Switch and Wii U: At Launch: 3 new treasure chests: Link Switch shirt and some useful items. Summer: new Cave of Trials challenge, a new hard mode, and a new feature for the in-game map. Holiday: new challenges with a new dungeon and a new original story. http://www.zelda.com/breath-of-the-wild/news/special-announcement-from-eiji-aonuma
I'll probably wait to see how substantial the new story is. The rest of it is just seems like filler to trick you into paying for it 9 months early.