With Sig's talk with Kal and what we know he's going to end up as in The Sunlit Man, alongside how tempting it is to have Dalinar as Odium's champion, I wonder if Stormlight 5 is our Empire Strikes Back.
Sig fails the windrunners, Kal dies (the goodbyes feel so final), Dalinar falls to Odium and we're left with with a small group to pick up the pieces and perhaps find some way to fight back in books 6-10.