okay, well, i was also thinking about orochimaru at the time and thought that maaaaaaaaybe, madara is really orochimaru, and he lost his sharingan along the way. so you kinda see why he was persuing itachi and sasuke.
well, you're probably thinking "you're an idiot, stop typing these stupid theories."
sooo, in verdict, i also thought of a different theory.
my other theory is this. the Living Corpse Reincarnation jutsu isnt really oro's own jutsu, its madara's. soo he was going door to door in different bodies and finding little old obito's. he is still an uchiha, it would be less hard on the body (for the sharingan).
---see the itachi-kakashi fight if you dont know what i mean---
sooo, in conclusion, i acctually prefer the second theory. because (parcially) both theories on obito and madara being tobi are correct.
so here is my lovely new theory. yell at me if you think its wrong, or give kudos to the cheif. (me)