Heres MY complete split theorum
A shortened version of the theory i lost after writing it for an hour was that Madara is both of them...
Tobi is madara's memories in Obito's body, he would lose his own techniques as his original body was probably dying (old age?) but he would have Obito's technique Space Time Jutsu and the implanted DNA sample, from Madaras fight with Hashirama at the VotE, this would give him the ability to use Izanagi freely and ultimately Banbutsu Sozo, once he had his rinnegan and his plan was complete.
He made a plan long ago to unite his soon to be dead body ie edo tensei'd madara and EMS, with his new Tobi body, so that he could use EMS, Izanagi, Space Time Jutsu, Banbutsu Sozo and control the Jubi once it had been gathered. Essentially the sage of the six paths reborn plus his own EMS.
However he was meant to be reborn with gedo rinne tensei ,but Nagato uses it on the people of Konoha instead, thats why he talks about Nagato as it was part of his plan, Tobi adapted when the snake shows up, it fits in as he can revive his old body that way ie impure world resurrection. Sasuke was a sacrifice he was willing to make to gain ultimate power.
Madara mind is inside of Obito's body
Obito's body is Tobi, thus all the similarities.
Madara is Tobi.
Tobi was created by madara on his deathbed to gain the abilities of both paths, look at this:
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Once he had gained both sharingan and rinnegan into a single body he would be able to use izanagi which can turn reality into an illusion and illusions into reality. But he no longer has his EMS powers, which is why Nagato was given the rinnegan, to resurrect Madara and combine EMS with Izanagi.
This is where it gets interesting if you read
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you see that madara wants to use his EMS genjutsu, that itachi talks about when vsing sasuke. His genjutsu is infinite tsukiyomi, if you know what tsukiyomi does you know that you control space and time, this means you are a god in this genjutsu controlling everything in this realm, by reflecting it off of the moon he would be casting a genjutsu upon every one in the ninja world. Once combined with Tobi and Izanagi his infinite tsukiyomi could be taken to the next level.... it would not only be a genjutsu in the mind of the person, if he used izanagi with infinite tsukiyomi it would turn the illusion of Madara/Tobi being a god into reality. He would have total control of the entire world.
Madara is Tobi and his plan to rule the world has been accumulating since the time when Konohagakure was being created.
I also had a thought that tobi may in actual fact have known that Kabuto could use edo tensdei, he may have known because zetsu is a master spy, who knows what he tells tobi and therefore had edo tensei as his backup.
If he did know that Kabuto could potentially resurrect the body of madara, but that it would be under Kabutos control would give him reason to find a way to gain control of it... Thus tobis fascination with Shisuis infamous Kotoamatsukami.
If you see any flaws in this hit me up. EPIC !