silver and golden bros ate kiyubi flesh full of chakra befor kiyubi spitted them...Madara might have done same thing befor he got spitted by 10th tailed Beast
Lel, it's the other way round, Kaguya is the one using Madara as a vessel. Kinda like how Black Zetsu was used. Madara almost/Might have died from the sealing process, I highly doubt Madara taking over Kaguya. But then, considering Madara's experience in controlling Bijuus, it's possible.
Still, as far as a villain motive goes, Madara has already lost his purpose. So, the one who will actually be villain is Orochimaru. Madara might put a major dent in Orochimaru's plans before finally dying mirroring Obito's sacrifice showing his redemption. In his convo with Hashirama, he never got redemption for his actions.