TOBI said something about an Infinite Tsukuyomi at the Kage Summit and the ET-Madara had the same idea like of Tobi's or it's just a coincidence? Madara has an accomplice, and that's Tobi. And Tobi? I think he's a part of Madara also, imagine the Kyuubi detected Madara's Charkra Signature when Tobi released it from Kushina using a Sharingan. I think there's a Class "S", "Sage of the Six Paths" or "Senju/Uchiha Accesible" jutsu involved here xD. Just a thought, like a Soul/Personality Split Jutsu? Truth and Lie, Madara and Tobi, but the same goal. (Read through "Kabuto-Madara Conversations" in 562). And Madara stored his own body in a secret and highly access-protected Uchiha Box for future use. A well thought-out plan I assume. . I'm hoping for speculations from y'all. xD. Maybe one of us will hit a right one in relevance to the Naruto story line.
If tobi wasn't clone or creation of Madara, I
would go for older member of Uchiha such as Uchiha
Uchiha Izuna said to be madara
equal in every way. He probably has same ambition
as him. So, if its him i think after he gave up
his eyes he didn't die. Madara transplanted
him a new pair of sharingans. He helped Madara
with his plans. Before Madara died, Madara taught
him everthing and gave him harishama's cells.
Izuna being old, needed harishama's cell to
extend his life and was able to use Izanagi. Maybe
Izuna did die, but Madara used his rinnegan to
bring him back.
We never see Tobi use
his MS probably because his eyes are transplanted
and didn't activate it yet or can't.
Tobi supports Madara and has hatred for Senju clan
so likely Uchiha. So, tobi is izuna and is helping
My third canditate was uchiha
shisui but little far off. If it were him, Madara
found him, trained him, gave him harishama's
cells. The moon eye plan probably appealed to
shisui because Uchiha shisui is powerful Genjutsu
user. His obsession with Genjutsu caused him to
take sides with Madara. Although shisui had
different beliefs like naruto, Shisui believed
that Madara's plan will really bring peace if
he can control the whole world with his Genjutsu.
As far as his abilities, he is much capable as
Tobi because he is known to be one of most
talented in the Uchiha clan. Plus, he probably got
help from madara to obtain those powers.
In addition, Soul/Personality Split Jutsu thing, I
think there's a jutsu that divides age, time
and event itself. A young Madara and a dead one
both existing in the present Naruto time. xD This
is just an opinion