OK, I agree with everything but the bold parts. How do you know Kagami has no motive? We know jack about him. He's appeared in, what, 4-5 panels? With all of 2 lines of dialogue. He may have studied under Hashirama and Tobirama, but doesn't say much about his character. Oro studied under Sarutobi, and look how he turned out. I'm not trying to say Tobi is Kagami, all I'm saying is there's about equal evidence to support Tobi being Kagami as there is to the contrary: none. On the other hand, there are very good reasons to believe Tobi is not Kabuto.Here's who Tobi is NOT:
1. Obito - The timeline of when Tobi attacks the village would put Obito as a young boy. Obito was also killed by a bunch of big ****ing rocks. Obito also has no reason to hate anyone in the Leaf Village.
2. Tobirama - The second hokage was a Senju, a staunch supporter of peace and willing to sacrifice his life for Konoha. His final act before death was to name Hirzen Sarutobi as 3rd Hokage. Then he was killed by the Gold and Silver brothers.
3. Kagami - Was one of the ninjas who studied under Tobirama and Hashirama. Has absolutely zero motive to want to destroy the leaf village. It's a stretch for him to know anything about the So6P, let alone about Madara vs Hashirama, the Juubi, ect, ect, ect. You might as well say 'Tobi is Kabuto' if you think that Kagami is Tobi.
The only people who are left to be Tobi:
1. Izuna - Has motive and opportunity. The only thing that would stop him from being Tobi is if he were actually dead, which we don't know for certain.
2. Setsuna - One of the dissenters just before Madara was outcast. Also has motive and opportunity.
Edit: and yes, I realize the Kabuto remark was an exaggeration.