Madara's ultimate goal
The more I read, the more it seems Madara doesn't care about this fight at all. Even if Obito loses, he doesn't care. He hasn't made a single effort to defend Obito or the Juubi. This implies Madara knows what we don't: The Alliance is boned. They can't kill Juubi.
So what does Madara want? Flashback seems to suggest he's a proud, vain man. He probably wants more than to take 10 tails into himself. He wants to be God of the new World. Moon eye operation? Some bullshit he cooked up on the spot to manipulate Obito. Madara caring about "world peace" or "rin" is absurd.
Obito might be wrong in assuming Madara wants to take the 10 tails for himself. Possibly, Madara just wants to find a way to be the strongest person to ever live. Madara in the cave seemed seriously butthurt about losing to Hashirama, so maybe he wants to be greater than Hashi could ever be. 10 tails is probably a means to an end for Madara.
When he was fighting the Kage, he seemed bored (in the Japanese emote text, he was actually yawning). Seems like someone on his level is content to just sit back and let things unfold. He could probably kill Naruto and Bee with his pinky finger. Perhaps he just wants to capture Kurama and relive the old days. Madara seems motivated by violence, so perhaps the war and immortality was his goal all along.
It'd be epic to find out Madara already has what he wants: an immortal body. That he planned for Nagato to betray Obito and for Obito to start the war, all for the sake of his amusement. Then he reveals to a dying Obito that he killed Rin, takes his remaining Sharingan and kills him right in front of Kakashi lol