I'm gonna stick with the "danzo is madara" theory. First of all, Danzo's right eye is a sharingan and you've only seen Madara's right eye sharingan, not to mention the fact that Danzo seems to have all the same information as Madara. Second of all, to reply to the above post, Danzo/Madara probably planned on killing all the other Kages at the meeting anyway. If he has Sasuke kill everyone at the meeting, Danzo won't have to reveal himself as Madara until everyone else is dead. My guess, Madara claims it's Sasuke's final mission because, when Danzo reveals himself as Madara, he plans on killing Sasuke. With sasuke and all the Kage's out of the way, Madara can rule over all the ninja nations.
At least, that's probably the plan. You know it won't go down like that. Naruto will come to the rescue and likely save the raikage by fighting Danzo/Madara alongside Sasuke. Blah blah blah, alliances forged, blah blah, naruto becomes 6th hokage, blah blah, the series becomes Konohamaru Shippuuden.