Kishi is clearly hinting that Obito is part of Tobi's mystery. It doesn't make sense that Tobi IS Obito because to too many reason that have been repeated here ad infinitum. I agree with whomever said that Tobi could Obito's father (possibly Kagami) for many reasons. He would have motive to hate the leaf and side with Madara's perspective on the leaf/Senju, due to Obito's death not being prevented. He would know Kakashi and Guy personally. He could either have taken Obito's remaining eye, or the family might even have the same ability innately and it was passed down to Obito, just wasn't usable until Kakashi implanted it.
There are some mysteries that if revealed might give us more information on Tobi, Kakashi and Kamui. How did Kakashi unlock his MS when he's not an Uchiha nor having to kill his brother? Why does Tobi not seem to need a MS, but is able to use STM/Kamui though Kakashi requires it? Just what/where is this alternate dimension that Tobi and Kakashi are able to access?
While everybody is concerned about Tobi's identity, what has really been bugging me is Zetsu's identity. He seems linked to everything somehow and I think that finding out his history will reveal much much more than knowing Tobi's. We know Zetsu is somehow connected to Hashirama Senju, the Gedo Mazo, Tobi, is one of the absolute first members of Akatsuki, has completely unique abilities including becoming part of the land itself, and has two independent parts seemingly representative of yin and yang. Most importantly we haven't been told ANYTHING about his history.
As far has Kakashi running out of chakra and dying or being KO'ed by overuse of Kamui. I think that he's practiced enough now that he can simply use it much more efficiently than previously. We've seen this being the case with many techniques in the series. As for blindness, that's a tougher one. Maybe Kamui isn't a MS technique at all. Tobi is able to use it without a MS and it seems to not be a significant chakra drain on him at all. Perhaps Kakashi is starting to match Tobi's efficiency with the tech.