[LET'S END THIS] Madara is Tobi, Madara is Madara.
Now, I'm not going to go and try to come up with all my theories through one way or another, I'm just going to base them on probability, and what is clearly stated in the manga. I'm not going to put my own concrete theory, just something for you and I to ponder with.
I based my theory on that, Madara is Madara, and Tobi is Tobi, on character's personalities and facts stated by characters. How I know Madara knows about Nagato is difficult to prove so I'm going to leave it up to you.
I have really considered that Tobi could be Izuna or other Uchihas for that matter, but seeing this just makes me doubt those theories to be true.
Tobi has always told the truth, we cannot prove this, but what comes out of his mouth seems reliable. His revealing the truth about Itachi for example, I see no reason for Tobi to lie and he willingly came to speak to Naruto about the history of the Uchihas and Senju.
You must be registered for see images
Either its Izuna, where Kisame mistakes him for Madara, since they're brothers, or it really is Madara. Again, I doubt Madara had his mask then, since he showed his face to Kisame, and in Akatsuki Kisame would of known it was Madara who was Tobi. Keep in mind that Kisame is a lot younger than Madara, thus, it is not the same undead Madara from the coffin. We also know its the same Tobi because Madara mentions making a place where he belongs in the previous chapter. (Sorry I didn't want to post the pic because it looks too long) I don't know if Madara can't or doesn't want to activate his MS, or he doesn't have EMS and doesn't want to use MS, since we haven't seen him use it once, we know he's capable of using genjutsu at the very least. I believe the EMS went to the undead Madara but that's just me.
This is a picture of Madara with Tobi's mask, it could be some other Uchiha, maybe Madara's brother, but he has Madara's hairstyle, and never in the whole series of Naruto have I seen someone change their hairstyle to something completely different, besides Tobi and old people. lol
You must be registered for see images
Here is more proof that Kisame recognizes Madara.
You must be registered for see images
This shows Itachi acknowledging it was Madara who helped him kill the Uchihas. Itachi is a genius, he surpasses the word genius, he wouldn't be fooled by an impostor.
You must be registered for see images
You must be registered for see images
Itachi even knew Madara as his teacher, he knew he controlled the nine-tails, which turned out to be true, he also states that he's immortal.
You must be registered for see images
I think this is what Itachi meant..
You must be registered for see images
This could explain what Tobi is, a shell, he's fully aware that he doesn't have much power anymore. His real body was the one that was revived. I can't explain why they have separate souls, but then again, clones have different personalities.
And the fox knew he was being controlled back then, he knew it was Madara. If Madara was dead all this time, would the fox be confused that Madara was someone else?
Just some food for thought, this really points to the unlikelihood that Tobi is someone other than Madara. I'm sure Tobi and most importantly Kisame and Itachi wouldn't lie.
The other theories are up to you.