For all those who believe Tobi = Obito
Alright, I think Kishi is doing this on purpose. Right when the Obito = Tobi theories were about to die down, he through some oil on the fire. So I am here to simply explain why Obito could be Tobi, but then lay out the final few things that simply halt the thoery.
Evidence that Obito is Tobi:
There are a few things that would lead us to believe that Obito is Tobi. Firstly, it's the name. Obviously, "Tobi" is very similar to "Obito". Secondly, when we first saw Tobi, he acted immature and he only showed a single eye, which conveniently was on the side that Obito would still have. Then theirs the hairstyle and the color of his first mask. These were the initial things that would lead us to believe that Tobi = Obito.
As things progressed, we saw more and more evidence such as his visual jutsu. This is really a big one, the fact that Tobi can use a wider range of Kamui. This is all fine and well. If this was all we knew, it would be clear that Obito=Tobi.
Evidence that Obito is NOT Tobi:
He lacks... motive! Yes. Why would nice, loyal, prideful Obito decide he wants to cast a giant gen-jutsu over the world?
Age. Now... this doesn't work if (as I believe) there is more then one Tobi. Firstly, Tobi seems to have connections to Madara, as in, before Madara vanished after with Hashirama. Secondly, He would've had to have acquired a vast range of Jutsu since the time he supposedly died and when Tobi fought Minato. These techniques included extracting Kurama, his 'ghost' ability and mastered that chain tai-jutsu.
Thirdly. Even if Obito DID harbor some grudge against the world, why on earth would he help Itachi take out the clan that he had so much respect for? Why would he want to control Kirigakure? It just doesn't make any sense.
Unknown factors that I believe Kishi will at some point elaborate on:
-The fate of Rin.
-Kakashi's possession of the Mangekyo Sharingan
(I find it unlikely that Kishi would place Kakashi Gaiden right between part 1 and 2 and in the first arch of part 2 expose Kakashi's Mangekyo Sharingan and his second closest friend just dropped of the face of the earth.)
-A biography of the sons of the Sage of Six Pathes.
-How Tobi gave Nagato the Rinnegan
-What exactly Zetsu is