Hello, spammers. I wanted to point something out.
1. Japanese Romaji syllable "to" means:
"
to: 10 (num), 18 litres (a measure of volume)

, door (Japanese-style)

, gang, if (conjunction), metropolitan (adj-no,n), municipal, party

, person (suf), promoted pawn (shogi) (abbr), set, ten, way

"
2. "Bi" is an ending used in the composing of adverbs.
Ichibi= one-tailed
Nibi= two-tailed
Sanbi= three-tailed
And so on, and so on.
Tobi= ...
Now, "Tobi" is just a pseudonym he came up with, we figured that much. It definitely indicates his intentions, though.
We MUST NOT ignore that half of the Kyuubi's chakra was sealed in Minato, and the other half in Naruto, therefore, as chakra CAN be divided and sealed separately (as we have also witnessed it happened with Muu's), half of Madara's chakra could have perfectly been sealed while the other half remained in the mortal world.
I still think Tobi is Izuna. I believe Izuna, in order to have Madara achieve the Rinnegan - seeing as he had a clear mind, defined intentions, and the leadership needed to achieve them -,voluntarily gave his eyes to his brother and then got another pair. Madara and Izuna had to turn to finding a proper vessel for Madara's Rinnegan once Madara was gone: this they did, possibly, when Madara was already in his deathbed. The result was Nagato, who then Izuna would drag into Akatsuki along with Yahiko, all of this to, at some point, once Nagato's abilities had developed properly, resurrect Madara.
Then he'd pluck Nagato's eyes out, again, to have Madara look pretty once more.
We MUST NOT ignore a döjutsu can be deactivated and still look peculiar (have you paid enough attention to the Byakugan users? Also, Kurenai's eyes are funny-looking - the older son's eyes looking like that DOES NOT indicate his jutsu was "on"); the older of the Sage's sons could have perfectly had it resting "when the picture was taken", though I really doubt the drawer would show him that way while trying to illustrate how he "inherited the Sage's *eyes*" <--- We MUST NOT discard the use of metaphors by the author, it would be very silly. It could perfectly mean he inherited the Sage's "vision", while "the youngest inherited the Sage's body" could mean he inherited the Sage's "mission", his fundament, his purpose, which completely makes sense.
The older son's eyes could also be a diminished version of the Sage's Rinnegan, which DOES NOT discard, at all, that he had the potential to develop the original Rinnegan, just like an Uchiha would (with the pressumed possession of the younger son's proper genes)
I think Madara, not Izuna, intends to become the Ten-tailed beast's vessel, BUT, in order to deceive his fellow ninja, Izuna needed to dress himself in uncertainty as much as possible, thus, when his identity was discovered (that is, when they discovered he IS NOT Madara but somebody else, still unknown), he would still be protected by his surroundings' ignorance AND Madara's intentions would still be unknown to them.
But that's just my theory.