User blog comment:Xilinoc/Ch. 605 - Don't Call My Name/@comment-11293956-20141113160904/@comment-2220112-20141114165944

Kamikake is a ritual to see into the future. Apparently they knew that Yhwach's target was the Soul Kings Palace all along. Shunsui remember went to the human world and told Ichigo's friends that he might not be able to return to the human world when everything was said and done, now it makes perfect sense that he would know to do that, just as well as sacrifice a for Kenpachi to get stronger.