Why didn't Kabuto summon Kushina during the war? Her chakra chains would have been a major opposition to Naruto and Kyuubi after all she was capable of restricting full powered kyuubi just after extraction and giving birth. At full power she would have proven to be a tough challenge. I mean many other fodder ninja were summoned so why a game changer like Kushina was ignored? It would have been a major emotional blow too.