Spoiler alert!
Ok, so I've got a few theories I'd like to share regarding Tobi, tell me what you think
it started when I wondered why kakashi couldn't use Amaterasu or susanoo or any other badass uchiha techs. And then why sasuke couldn't use kamui. This leads me to thnk the following; that different uchiha have different abilities with their mangekyos. That however is discounted by the fact that both sasuke and itachi can use Amaterasu, susanoo, etc, so I think instead that close family members can use similar techs (but with different successes, such as sasukes superior Amaterasu compared to itachis).
Finally, I've always wondered about the similarity between kakashi's kamui and tobi's techs. At the time he claimed to be madara so I didn't think too much of it. But now we knw that isn't the case and (as supported by the latest chapter) Tobi is using kamui too into the same dimension, this could support the there that Tobi and obito uchiha are the same person. This however is disproven by a multitude of data, particularly obito's apparent death and his define loss of an eye which Tobi had in order to cast Izanagi. This leads to three theories;
1. It's a relative of Obito, maybe a brother or father, who shares his ability
2. It's a Zetsu clone of obito, who has all of his abilities (and obito actually sympathised with the uchiha rebellion)
3. It is obito, he somehow survived being crushed (zetsu's doing?)and the eye that was lost to Izanagi was taken from another as yet unknown uchiha prior to the rebellion.
Anyways, what do we think?