Tobi wanted Nagato to use rinne tensei for his purposes, we didnt know what that was but with Madara now thinking initally he was revived by nagato's rinne tensei it appears Tobi wanted to revive his brother Madara all along. Very important to note that madara wasnt pleased that he was revived under the nototion of it being Nagato, showing that he must have feared that Nagato could have gone rogue and deviated from tobi and his plans. Last chapter Madara was talking about a person that had plans for his revieval which didnt quite go right. Kabuto steps in and tells him he is the one controlling these summons and that he was this person's assitant. Both madara and kabuto are talking about tobi I guess so this just adds to the mystery of tobi.
But Kabuto has ruined tobi and madara's plan, looks like tobi is rushing to Madara right now to make sure Kabuto doesnt turn madara against him. And we understand why Tobi was shocked to the point of calling kabuto a madman because how Kabuto got MADARA's DNA now is A MAJOR TALKING POINT. I can only assume Orocihmaru will play a role in his from the past afterall he was obessed with the sharingan so why not try and find the greatest uchiha to ever live, makes sense to me. Orocihmaru has already graved robbed hasihrama's body why not Madara aswell. Making me wonder what Orocihmaru's true goals really were.
Very important thing to note is the era of madara's death as this too is strong evidence that Madara and his borther tobi have made plans to take over the world. Since Madara knows about Nagato and rinne tensei that means Madara died around the time when Madara was pretending to be the muzikage. The hair styles match aswell of edo tensei madara and madara behind the muzikage when he first meet kisame. But all the way through this time Tobi was also alive at some capacity remember he wouldnt have regained his eyes probably until Madara gave them back to him during his final hours. Tobi(pretending to madara) said he did take hasihrama's cells, so with Hasihrama cells I can easily see how both Madara and his brother Tobi have stayed alive as long as they did.
Also some portions of the confession to Sasuke about Madara's actions in the past by Tobi is also VERY important to note. Tobi(pretending to be madara) said he didnt take his brother's eyes BY FORCE, now I totally belive this and during this time Tobi clenched his fist in anger when it was suggested Madara stole his brothers eyes. And it makes prefect sense why Tobi has a big grudge on konoha and the uchiha like Madara did because when Madara took his brother's eyes the clans uchiha and senju made a truce and the sacrfice was in vain. Not to mention Tobi's more recent actions being the Fox attack on konoha and his dealings with itachi/danzo to wipe out the uchiha clan.
Another thing that is making this very belieable is how much Tobi knows about konoha,uchiha, senju,rinnegan,so6p and more importantly Hasihrama. Not to mention jutsu in general, we see Tobi being incrediblly well knowable in jutsu. Also out of the abilties we have seen Tobi use his strong genjutsu skills relates back to the Sharingan and the Uchiha. Also Tobi talking over the fox against minato is a clear sign Tobi was once a MS user but more importantly that Tobi is an Uchiha and a strong one. Also all that Tobi talk about being a former shell of his former self fits in with Tobi being Izuna as he gave his eyes to Madara and weakened as a result.
At this point Tobi has fooled everyone including both Minato and Itachi quite well, because pretending to be a dead man's brother is a hard cover to break if you dont know much about Madara to begin with. For example if Tobirama and Hasihrama were alive Tobi wouldnt have fooled them as they know Madara all too well as they are all in the same era. Even Onki being as old as the third hokage was inaitally very surprised Madara was still alive at the kage summit, but even he had to accept it as true dispite actually fighting Madara. I feel Madara fought Onaki around the time Madara was controling the Muzikage. In fact next chapter PLAY CLOSE ATTENDTION TO WHAT ONKI COMMENTS ON MADARA'S MOVEMENTS AND SKILLS.