User blog comment:Omega natsu2/Chapter 364: Tartarus Arc, Part 1: Immorality and Sinners, Predictions./@comment-7418318-20131211093800/@comment-1359322-20131211100355

Hmm well a bit of correction is needed in what you said:
 * 1) Naruto was fighting against Madara in his Kyuubi Mode.
 * 2) Kakashi and Minato are being pitted against a Zetsu-controlled Obito.
 * 3) Tsunade is still recovering from her injury in the battle against Madara, and Gaara was fighting along Shuukaku, so only 3 Kages are missing.