Thinking about it, a flashback or two will probably be necessary. A lot of Naruto villains, especially in Part II, had their character built around flashbacks to the point that they were interesting (Sasori, Madara, Deidara, Itachi, are some examples). People are objecting to the idea now but the fact is that villains like Obito or Madara would not have been even a third as interesting if flashbacks didn't set up their characters to where they are right now. Chances are, we might need a flashback if we're ever going to at least understand Kaguya's intentions and motivations.
