"Tobi could be Kagami Uchia.First of they kinda look the same.He is old enough to have meet with Madara, he got the name tobi from he's teacher Tobirama, that learned him Space time teq. We know that kagami could get the intel about the leaf village so he could get passed the barrier and get to minato. But clearly it's some one that Madara had made plans with if you have read 560 where Madara says "PLANS" like he know's what going on like this was a backup plan if he were to die. My theory.^^"
OR
(Izuna could be Tobi but his body is a CLONE! He needs the 10 tailed beast to be complete again! Nagato was supposed to help Tobi to revive Madara but Naruto convinced him about his plans, then he used the Gedo Jutsu to revive the leaf village this is why Tobi was pissed of at him and Konan! Tobi needed Nagato to use the GEDO Jutsu for Madara!
Kabutomaru revived Madara in another way and it took longer 4 the plan for Madara 2 live! Madara mentions " I see things didn't go quit as planned"!)
I agree with these two theories, is one or the other.
Tobi /= Spirit lol