Right we've heard all the theories so far and i've been pondering on this one having thought that izuna was tobi (still a possibility) ok right here goes...
What if....izuna and madara are both still alive?Izuna lost in a fight with Madara and is left with only one sharingan eye (danzo) then madara is tobi gaining ems?Izuna wants to get revenge on madara and wipe out the uchiha so takes the identity of danzo?Makes the order for itachi to take them out?This would go in sync with the brotherly feud that was had between sasuke and itachi? And them both wanting power? I know this is out there but think about it!It's actually possible! (I'm thinking outside the box and thinking of something different here!) I know people seem to be leaning toward obito right now with the arm but it just doesn't seem right with danzo's age =/ as this would mean he is the same age as kakashi?
(actually I believe it was said kakashi was older than obito and rin aswell
) But yeh this is another one to think about and I thought I would mess with some peoples minds again 
What if....izuna and madara are both still alive?Izuna lost in a fight with Madara and is left with only one sharingan eye (danzo) then madara is tobi gaining ems?Izuna wants to get revenge on madara and wipe out the uchiha so takes the identity of danzo?Makes the order for itachi to take them out?This would go in sync with the brotherly feud that was had between sasuke and itachi? And them both wanting power? I know this is out there but think about it!It's actually possible! (I'm thinking outside the box and thinking of something different here!) I know people seem to be leaning toward obito right now with the arm but it just doesn't seem right with danzo's age =/ as this would mean he is the same age as kakashi?