A while ago I began an insistence that Zetsu (specifically the black Zetsu) is actually the big bad, and is actually
actually the one pulling all the strings behind strings. For there to be one more bad guy "behind" everything isn't unbelievable, it happens all the time in the Narutoverse. My fan-wank theory had something to do with Zetsu's true plan for this war to be to spread himself across many places in the world, 'sewing the seeds' as it were for something involving the jyuubi. I had gotten it into my head that Zetsu was the consciousness of the jyuubi. I have no idea where to look for those posts, but I was proud of my insane ramblings.
My original reasoning for this was that we know less about the black Zetsu than really anyone else in the series, and I thought I was dealt a horrible blow in that
one chapter a lot of people didn't like. I thought "Since black Zetsu is so young, he couldn't be the one that started all this crap."
Months later, it hit me. This is actually proof of my near-random idea.
The before-mysterious "black rods" got the exact same cripplingly over-simplified origin as being "the will of Madara". My current idea is that what Madara said is bullshit. He has no idea what the black rods are and just like Nagato, has no idea what they really did to him when Gedo Mazo (presumably) synced with him. But the reader does have an idea of what happens:
even the gentle-hearted Nagato looks fucking crazy with power, almost instantly. I'm going to go out on a limb and assume that Madara was transformed from someone who, while being frightfully powerful, was only about as much of an aimless asshole as Sasuke until he summoned the Gedo and (probably involuntarily) synced with it. Then he suddenly 'got the great idea' to revive the jyuubi. This would make Madara look as if he was dicking around with something he didn't understand, and he would (FOR ONCE) have to eat his own words about people abusing forbidden jutsu and the like.
My conclusion- the black rods are the will of the jyuubi, and the jutsu that Madara did to create Zetsu has nothing to do with "Madara's will", aside from that which overlaps with the jyuubi's own will. The black Zetsu is the black rods given human shape via Yin/Yang release. Further, since the white Zetsu all were grown from Gedo Mazo, and black Zetsu can merge with them, maybe he can merge with the Gedo itself, and by proxy, the jyuubi.
I wonder when we'll see Zetsu next. Man he sure got beat awful quickly

Either he's waiting for Ivysaur jyuubi to evolve into Venusaur jyuubi or I fear I may be wrong. Also this theory being right would make
his appearance here all the more poignant.
PS: This may also be why Tobi seems to have chosen not to sync with Gedo Mazo, and was instead attempting to get Sasuke to. He already noticed the influence from being merged with the white Zetsu (a creation of the Gedo), and didn't want to involuntarily lose anymore of his humanity than he already did. Or maybe he just couldn't. Idk lol
Bonus off-topic prediction: Tobi has two distinct personalities, like Zetsu.
The mask reveal was a red herring for his true 'traditional bad guy body modification reveal':
Sasori - really an adorable bishie inside of a tank monster
Deidara - fucking awesome chest mouth
Hidan - didn't need one; he could survive decapitation and that's good enough for this list
Kakuzu - the heart masks
Zetsu -

Itachi - the only clean one; makes sense since he's not a bad guy
Kisame - special case, his 'reveal modification' wasn't under his clothes per se, but in his sword
Pain - another 'different' one; Nagato, the 'real one' was the reveal itself
Orochimaru - sheds his skin to reveal the White Snake
Madara - had his armor blown off to reveal Hashirama's face
Kabuto - Snake sage mode counts, I guess
Tobi - Spiral Zetsu is still attached to him. When he was being cooky, fun Zetsu, that was spiral zetsu. It has since merged with him more completely, enabling him to spam the shit out of his version of Kamui. When his shirt is blown off completely we'll see his monstrous abdomen, probably complete with a talking Zetsu face that can move around on his body and cover his Obito face when it wants to take control.