* The Tobito part is more to fuel that ancient theory that still has quite a few followers. And because we know a lot about him, we saw him as a young Naruto like Uchiha. And the future reveal to Kakashi would fit story wise. It would be a "WTF" - moment. And it can still be true in some way or the other, although the probability is less than Tobi being maybe Izuna, Madara's younger brother or Kagami, the young fellow in Tobirama's squad with Sarutobi and Danzou, (age wise hes there). There are still Uchiha Shisui believers and even Fugaku, Sasuke and Itachi's dad.
* We know that Uchiha Madara got some of Hashirama's "powers" in his fight with him. That was the sole purpose of their fight for Madara. He took his cells. With this he could become the 2nd Rikodou Sennin. He had obtained Mangekyou Sharingan, went blind and later took Izuna's eyes and obtained EMS. So the theory is; after infusing himself with Senju it is believed that his EMS turned into a Rinnegan. And if you give the EMS to a strong Senju body, Uzumaki Nagato, the person will activate Rinnegan. So to give more meat to the Madara's brother is Tobi theory, Tobi said that "he" gave Nagato the Rinnegan. Tobi also said when taking Nagato's Rinnegan that he just took back what was once his. Izuna's Eyes -> Madara's EMS -> Nagato's Rinnegan. But I'm not a big follower of it being Izuna. Since that wouldn't be a "WTF" - moment when seeing him without the mask. The possibility is there, but not the probability. There are a few more arguments about Tobi being Izuna, but I can't remember them atm.
* If Tobi really is an Uchiha then I wouldn't be surprised if he knew this, since the Uchiha's have been known to know a lot! Especially since the story is about Uchiha vs. Senju. Thus Izuna would be a real goldmine if he were Tobi. But I have no idea how he could have stayed alive for so long
I think the key to finding out who Tobi is, is to correlate the different timelines of both Tobi's and Madara's apperances in the story. The long hair/short hair correlation when introduced to Kisame and Itachi, the attack on Konoha. The different masks. The part how Zetsu is involved in Tobi's body. There are a lot of mysteries and I hope that Tobi's reveal will be something real special, because there has been quite a buildup.