Welllllll...
iiNo Empathy
1)It is revealed that Tobi must be of old age which is why it can't be Obito or anyone around that generation
As old as Sarutobi and Onoki were (baldness, grey hairs, liver spots and pools of wrinkles) I doubt that Tobi could be from that generation.
iiNo Empathy
2)If Izuna Uchiha was second to Madara why hasn't Kabuto used Edo Tensei to bring him back...because he can't since Izuna(Tobi) is not dead.
This I can't really dispute.
iiNo Empathy
3)Right before Madara dies he unlocks the Rinnegan. Have you ever wondered what happened to Madara's eyes when he died? They were implanted to Nagato and so forth. Before Tobi fights with Konan he clearly states to Konan that the Rinnegan is not Nagato's it's he's(Tobi). When he said that I just knew who it was. Think about it the Rinnegan Nagato had was actually Madara's eyes. Tobi says its his eyes because Madara took his younger brother's sharingan and whose his younger brother IZUNA UCHIHA.
I imagine Tobi, whom was acting as Madara, said this in account of if he were truely Madara, those would literally be the eyes that last left his sockets.
I have my chips on Setsuna Uchiha.