I've spoken before on my creative process. I build books out of good ideas, often developed in isolation until I find the right place for them. (Allomancy and Feruchemy were originally developed separately, for separate books.) When a book doesn't work, the ideas get broken apart and bounce around in my head some more until I find another place to try them out.
Bridge Four—and the plateau runs—were originally part of Dragonsteel. Dalinar was too, so that's not all that surprising, I guess. However, Bridge Four is unique here in that when I decided to move them from Dragonsteel to The Way of Kings, I had already completed both books and felt pretty good about them. They are both important sequences in the Adonalsium Saga, and lifting Bridge Four from Dragonsteel meant taking away its most dynamic, powerful plot structure.
That decision was not easy to make. The problem is, both books were fundamentally flawed. Oh, they were both good, they just weren't great—and I felt I needed to be doing great in this point of my career. (Hopefully during every point of it.) The Way of Kings had an awesome setting and some great characters, but no focal plot sequence that really punched someone in the gut. Dragonsteel had wonderful ideas, but they never really came together.
In the end, I took the best part of the book that otherwise didn't work and put it into the book that needed a little extra oomph. The moment of decision came when Ben McSweeney, who was doing concept art on the book, sent me a concept he'd done that looked shockingly like the Shattered Plains. (Which, remember, were not even on that planet at that point.) I realized that they would fit the worldbuilding of The Way of Kings better than they ever did Dragonsteel, and that I could put greatshell monsters in them.
So, I ripped apart a book I love to make a (hopefully) better book. Rock came along to Roshar for the ride (he was an original member of Bridge Four in Dragonsteel). I added Teft, who had been left languishing for a decade or so after Mythwalker became Warbreaker and he didn't make the jump. Bridge Four seemed like a great home for him.
[Assistant Peter's note: Teft is mostly the same character as Hine from Mythwalker, but also has a character aspect from Voko in that book.]