I personally think that Danzo and Madara made a deal of some kind back before the destruction of Uchiha, Madara gives Danzo his left eye (to be implanted) and Danzo brings up the idea of using Itachi to destroy the Uchiha clan to the counsellors and the third.
Since all shady parties involved seem to enjoy using other people, they could all be trying to use the events to their own end.
Example: what happened to all the dead Uchiha left over, If "someone" knew there would be alot of unused sharingans were to be lying about, what you they do with them.
So Danzo might not be Madara, Obito, tobi or Madara's brother.
Still, I don't claim to know anything, this is all predictions and theories.