Nice theory

I always wondered why neither Madara nor Obito showcased the all power of the Six Paths jutsus that Nagato had (which are named after the Six Realms). Perhaps this idea will come into play later because right now we have no explanation of where Kaguya came from or what she wants to use this Zetsu army for.
Maybe Kaguya and her sons represent the God Realm. And as you stated in the OP, she currently has complete control over the Human and Animal Realms. Naruto and Sasuke could represent the Asura Realm, as they are in direct conflict with Kaguya (God Realm). Kaguya would have wanted to use her army to further conquer the Hungry Ghost and Naraka Realms (whatever they may be).