User blog comment:Xilinoc/Ch. 581 - THE HERO 2/@comment-6073876-20140522171212/@comment-10630156-20140523122754

From what Shinji said it appears that Ukitake isn't back yet from his little journey. As for Shunsui it appears that he was stalling for time until the likely reinforcements arrive capable of fighting off the more powerful quincy (Jugo ect) he is probably aware of who all the Special War Powers are and is waiting for them all to gather before making a definitive move against the Wandenreich.