I'm not as familiar with the cosmere stuff as the rest of you, but just from this alone...
Child of Tanavast. Child of Honor. Child of one long since departed. The sudden voice shook Kaladin; he floundered in the air.
The Oathpact was shattered.
Could Tanavast be the name of the Almighty? Or at least one of the shards/shardholder dudes? Or is Tanavast something in-world?
I mean, "child of one long since departed." We know the Almighty is (likely) dead and that he made humans on Roshar, and we don't know for how long he has been departed... but considering the most recent vision we get to see from Dalinar is the day of Recreance, that would certainly be a long time ago.
So then, "Child of Tanavast" and "Child of one long since departed" could be the same? And could the Almighty be "Honor"?
Or maybe Tanavast held the shard named Honor, and that's where Kaladin's magic (and maybe the Nahel bond) comes from?
I feel like there's something big in those lines, I'm just not sure if I'm looking in the right direction.
Edit -- More likely, perhaps Tanavast is one of the Heralds? The Herald of Honor? That might make more sense, considering the talk of the Oathpact.