Madara has been shown in the manga speaking to a mystery person, who was asking Madara to "let them in". The assumption is that this could be Kaguya, but an assumption is always just that, guesswork.
Everytime I hear that, I have a feeling of doubt. Looking at Madara's past, he was deeply involved in heavy fighting between Senju and Uchiha, and even after having seen such bloodshed, when Hashirama opens up and discusses peace between clans, and asks Madara how they can get along, Madara responds like this:
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Conclusion I reached, Madara's answer to peace is through revenge, and he is very much like Sasuke in this selfish drive.
I doubt Madara cares much about peace personally. I think it would be more likely (and this theory is pretty far-fetched) that he perhaps knows how to rewind time, and wants to rewind time to re-fight Hashirama/prove that he didn't take Izuna's eyes on purpose, or some other ridiculous Madara style gesture.
Looking through Madara's past, his life story is one desperate clasp for power after another.