I read a post sometime ago that gave me the idea that Tobi may really be The Elder Son. I went thru 90% of the manga and anime for any clues, similar situations, history of key techs and people. There is nothing directly pointing in that direction(yet), but, I did see that it is possible with what little I found.
Prediction:
Tobi is The Elder Son(TES)/Madara's body is in the 6th coffin.
To get to Tobi's identity... Process of elimination.
6th Coffin Candidates
1. Shizui, Izuna, anyone else you may think of.
They are all too weak to elicit a sign of weakness (surprise/fear) from Tobi. (Chapter 490 pg.4)
Despite any possible power-ups gained when summoned, there is no evidence of them gaining new abilities that could counter Tobi's current skill set.
2. Hokages 1-4
Unavailable due to souls being sealed by way of Shiki Fuujin. (Hokages 1-3 Chapter 124 pgs. 6-7; 4th Hokage Chapter 503-504)
3. So6P or The Younger Son
Possible, but, either one could defeat Tobi with their known skill set.
4. Madara
Most likely to elicit a sign of weakness in Tobi. Since Tobi is claiming to be him.
Tobi =
1. Madara
Possible, but, unlikely due to Tobi not having access to EMS. Outside of Izanagi he only has at least two Sharingan related jutsus... an advanced form of Kamui and genjutsu.
Madara was portrayed as one who valued his lifestyle as a weapon and sought to be the best weapon at any cost. (Hence the numerous battles leading up to the last one.) His eyes were never opened to the big picture before that battle.
2. Anyone else -
No reason to be worried about who is in the 6th coffin. Tobi's skill set is far greater.(other than So6P and his sons)See also 6th Coffin #1 (Note: Shisui is TOO young to be Tobi.)
3. The Elder Son
His intentions may be vague for attacking his brother, but simple to figure out. Losing to his brother he failed at one thing... Getting a sample from the original Senju. The Elder Son wanted the powers and abilities of his brother to become So6P. He believes they "belonged" to him and should have been given to him. Unlike Madara he saw the big picture about the world. His view of peace was power... to control the world. (Tobi's intentions mirrors The Elder Son's exactly.)
(As many times as Madara and The First fought not once did he get a(DNA)sample. But, the last battle was revealed to be a ruse just to get a(DNA)sample.)
Kage no ō
