Gotta admit this would be some kind of interesting outcome. But I wonder if humans can be sealed / eaten by the Mazou. Besides, Madara already said that he's going to extract the Bijuu out of their Jinchuuriki, meaning that Naruto's chances to be swallowed together with Kurama in the Mazo are less to none.
I always thought that a good way for Hagoromo to enter the scene would be through either Naruto's consciousness, but that would be too mainstream, or when the fully revived God Tree will reflect the Tsukuyomi on the moon, he, Hagoromo, who supposedly sealed his corpse ON the moon, would be revived and return on Earth. Sounds pretty fictional, but anything's possible.