Board Thread:General Discussion/@comment-25642086-20141108072343/@comment-1268838-20141108171541

Well, Isshin knew about both Auswählen and the Kaiser Gesang. Whether the Shinigami as a whole knew about them is unknown. Furthermore, we don't know how or for how long Isshin has known, though I suppose Ryuken is suspect.

Yamamoto and Mayuri's conversation earlier in the arc suggests that Yama didn't see this coming. Mayuri suspected, but they had nothing concrete to go on.