To my understanding, the sage said he was going to give Naruto and Sasuke what was left of his own power/chakra- not the sons' powers/chakras.
The sage told Naruto that Madara awakened the rinnegan by combining Indra and Ashura's chakras which in turn brought out his own (the sage's) chakra...
Well, Minato was the Hokage before the 9 Tails attacked, meaning that the Uchiha were planning the Coup D'etat during his reign- he must have been doing something wrong which he can tell us about.
I honestly doubt Kishi will show this to us though, Minato's too "clean" (for lack of a better...
Re: The Adventures of Hashirama's DNA 626 Spoilers Discussion
Isn't Izanagi only usable if you have "the powers of Senju and Uchiha"? (According to Tobi and Danzo) I don't think it's possible for Madara to have used Izanagi during the fight to escape, unless he somehow got Senju cells before...