Hagoromo said that a new fruit will be (/come into existence) if all chakra becomes one. Sasuke, Naruto, Obito, Kakashi, Sakura and the four Hokage still have chakra and Kaguya hasn't absorbed them yet. Because of this, I don't think we can definitively say that Kaguya is the fruit. Also, when Hagaromo said it'll be game over if a new fruit is spawned, I guess he means that somebody will eat the fruit and become a new Kaguya and the cycle will repeat itself. Other than this little theory, I like your theory and it does seem plausible.