Mostly just learning about the world itself. How everything came to be the way it is. The Mistborn trilogy made it clear that Brandon has a reason for everything. Though I don't expect to learn a whole lot in the next book.
I'm also a sucker for giant beasts, so I want to see more of those. That one interlude that was posted about the Reshi Isles has me hungry for more.
Also, more Hoid and Heralds.