There's a lot of planned intent discovered in this chapter.
The secret stone slab, contains the secrets to Madara's body but it's encoded. We all know Itachi and Sasuke have read this slab, so how much do they know.
Still even more, if the slab contains Madara's knowledge on the Rinnegan as he implies when he asks Kabuto if he did decypher the slab, then we can be sure that Madara had a plan, and an obsession with the Rinnegan for a while. Why would Madara keep a secret "diary" with the information on his body, if not because he already expected it could turn out disastrous.
From all this information, I even more strongly think that Madara had been planning to 'enhance' his own body for a while. Probably from somewhere around the time of his 'presumed' last battle with Harashima. Now, it's very likely he was left half dead after the battle, but somehow managed to pull through. Then he started experimenting with Senju DNA. Very likely this is where Zetsu came into the picture.
I seriously doubt that Black Zetsu was created using Senju DNA, that's where the white ones came from. I still believe Zetsu to be a fragment of the 10 tails and it is the driving force behind Madara. The 10 tails wants to return to its former state, and to do this it needs the power of the one who split it in the first place: the sage of 6 paths.
Think about it, how would Madara know that experimenting with both DNA could awaken the Rinnegan? After all, up to that point it was a legend (even the frog sages know nothing about it apart from it being a power of the old sage). How could Madara possibly know that he could unlock it?
Simple, the 10 tails was part of the sage of 6 paths, and thus knows about his powers very well. For it to recreate a sage, which can return it to its old form, it would need to know how to go about doing this. Logically, this would be to bring back the DNA of both his sons into a single person, in this case Madara.
It started getting complicated when Madara's body started rejecting the Senju DNA and he was essentially dying. Madara had been recording all these changes on the slab so far.
Now only the 10 tails could know that the Rinnegan possessed the power to return the dead to the living world. But even it (Zetsu) fused with the essence of Madara could not perform such a powerful Jutsu. So they needed to transfer the Rinnegan to a suitable subject. Nagato, being Uzumaki and thus with powerful chakra, was the chosen child for this and Zetsu would watch over this child to make sure he could eventually return Madara to the living. This would also solve the problem of Madara's bady rejecting the Senju DNA and would make him the next sage of 6 paths. At that point, he would return the 10 tails to its old form, and this incredible beast could rage over the world, with or without Madara. I'm sure the 10 tails is withholding info about how to seal it from Madara.
The eye of the moon plan (which is just a spiffy name for bringing back the 10 tails) was not a priority for Madara imo, this is Zetsu who has since then been looking into was to return its old self without the help of Madara, making sure it could not be stopped.
At this point, edo Madara is too powerful. He is in fact the new sage in an undead form. He will only be defeated by Itachi ending the edo, but not before giving away that Tobi has his own agenda by now and must be stopped. The series will end with Naruto and Sasuke, having to work together to equal the power of the sage, and seal away the tailed demon for good. Madara wanted to be strong enough to control the world, but doesn't want to destroy it like the 10 tails wants. From the history we know about Madara, he's all about getting power and making people follow him.
Well, just my 2 cents
