1) in manga chap 510 we c dat tobi has 2 sharingans hence possibility of tobi being obito is nil...
2) tobi is vry powerful so it can b considered dat he is uchiha kagami coz he was trained by 2nd hokage senju tobiramaalong with super strong teammates lijke sarutobi hiruzen and shimura danzo.
3) it is obvious dat tobi cant b madara coz a living ninja cant b resurrected by edo tensei...
4) uchiha kagami was the father of obito n obito died during the war....hence he considered the village responsible for obito's death hence in order to avenge his son's death n to create an absolute peace he resorts to use ten tail's power to place the entire world in an infinite genjutsu.
5)
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6)Read ch 510 carefully
7)It cannot be obito because he has already been regarded as a hero and it has led to his brave ending
8)Possibly no new character would be introduced as it would breaks the viewers anxiety.