I got this idea, and it's making me wandering. It's not complete, but here it is:
Madara prepares himself for battle with Hashirama. He gets Kyuubi, and he prepares a safety:
He tells Tobirama that he would help him become the Hokage if he resurects him in the case he dies.
He fights Hashirama and dies. Uses izanagi twice, and leaves no usable eyes behind.
Tobirama realizes that his brother is too powerfull, and that his genetics will grant him a long life. The only way for him to get his share of fame is to do what Madara proposed. He uses Edo Tensei and resurects him.
(Remember, Kabuto said: You were completed beyond your prime. Madara: You... know about my prime).
Part of the deal was for Madara to get Hashirama DNA, as his goal is to get rinnegan in order to resurect his brother. He should also stay hidden and stay away from Tobirama and Konoha, or else, Tobirama would release Edo Tensei.
Tobirama lures his brother to a remote location and, together with Edo Madara performs a stealth kill. Blames some other village, which starts the 1st great war.
Madara stays away from Tobirama, but in order to free himself from the possibility of Edo Tensei release, he hires merceneries - Kinkaku and Ginkaku. They fail the first time, but the second time they come with a larger force. Feeling guilt, and that he is no worthy of being a hokage, Tobirama sacrifices himself and chooses the most honest one - Sarutobi to be the hokage.
Madara awakens rinnegan and resurects Izuna. However, something goes wrong, and his spirit leaves the earth. They meet in the purgatory (where Kakashi met his father). Madara instructs Izuna that a boy Nagato could be host for the rinnegan and resurect him, since the process requires that the performer die. Izuna tells him about the Moon eye plan, which would free the world from war.
Izuna gets resurected, but with some bed eyes. Madara sticks in the purgatory, since his brother did not forgave him.
Izuna gives Nagato the rinnegan eyes, but gets a second thought about resurecting Madara. Maybe he should implant the rinnegan into himself and perform the MoonEyePlan without his power seeking brother. He starts experimenting with Hashirama DNA, but overdoes it, starting to loose ability to maintain his sharingan. He needs a new Uchiha body. He finds dying Obito...
In the purgetory, Madara meets with Obito's spirit, who tells him about what happened.
Now, for the 601:
Tobi was not happy hearing about Madara resurection. Madara called him Obito ironicly, and implying that he knows about his change of heart. The two of them will argue about what to do and finaly get into a fight.