First of all, that is a great post.
I thought Nalan was doing it in an attempt to stop the upcoming desolation, because he thought without surgebinders it wouldn't happen. Due to his code he could only go after people who had committed crimes. One of the arguements made by the Parshendi for trying Stormform was seeing Kaladin surgebinding so he may have been right. Those are my thoughts anyway.
It may be similar to Amaram seeking to bring back the Voidbringers in an effort to bring back the Radiants and return the world to more of a Hierocracy state. The spren came back because they saw something terrible coming, but maybe them coming back caused it?