I have an Orochimaru is a Senju thread, but I also like the idea on Tobi. The reason is because Tobi was able to control 6 tailed beasts with ONE Sharingan. This hints at godly amounts of chakra...A Senju body. Alto take into account Izanami's chapter. It hinted that the Uchiha used Izanagi on a massive scale, and I doubt the Uchiha all injected themselves with Senju DNA. It seems the Uchiha did not need Senju DNA, and that they did not permanently lose their Sharingan to it. Only NON-UCHIHA need Senju DNA and lose the Sharingan, which means that Tobi is like Danzo.
The level of hatred Tobi has for Orochimaru makes me think he could be a Senju Orochimaru experimented on...Someone that fits the timeline, like Nawaki perhaps.