Many interesting theories here, and some of them seem realistic.
I don`t think either Sasuke, Donzou, or Madara for that sake, can afford to lose. Someone need to show up and clean up, and i think that person is Itachi.
Someone keeps mention that Kishi has said that Sasuke will fall deeper into darknes after this fight, that?s wrong.
Kishi said that this fight will decide what will happend to Sasuke onwards. If he will fall deeper or if he will give up on taking his revenge out on all of Konoha or something like that. At least that is in some way what SacredSaberTooth said in the last prediction thread:
"The battle against Danzou will decide Sasuke's direction but he (Kishimoto) told us that he wrote something big happening with Sasuke"
He asked: "What will happen to Sasuke after fighting Danzou?"
「ダンゾウ戦が終わってサスケの今後の展開(行動というか意志というか)が決まる」
"The ending of the Danzou fight will determine Sasuke's coming development (whether it be his movement or his intentions)" and so on
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