This also explains why Orochimaru joined Akatsuki to begin with and also gives more of a reason for why he left. Orochimaru was likely looking for the ideal Uchiha not just to obtain the sharingan but as someone who he could join the bloodlines within. At the time Itachi seemed like the perfect candidate. Kabuto implied that Orochimaru knew that Tobi was not Madara and Orochimaru also probably knew that if he could get Itachi's body, with what he knew he could easily defeat Tobi and take control of Akatsuki. When Orochimaru lost to Itachi though he also quite likely raised Tobi's suspicions of him. So he lost his ideal test subject and also revealed his treachery towards Akatsuki as a whole.
Whatever the plan is, it sounds evil. I mean that might be why Danzo had all the Uchihas killed because he wanted to prevent whatever Orochimary had in store.
And what happened to Guy! With Naruto's chakra he'd be a badass. I want him open the final gate already!
A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools.