I think the gedo mazo has something to do with hasi though. i mean maybe madara created it with his rinnegan as a mistake because he was trying to make something to control the bijuus or he just didn't complete it. Then it got mixed up with hashi's DNA (it kinda looks like trees are on it's back) then madara was getting to old to finish what he wanted so he stop messing with it and around the same time gave his rinnegan to nagato and told him about the gedo mazo and told him not to use it as of yet unless you collect 9 bijuus then it shall be complete and it's power shall truly awaken or you will have a better power to revive him and maybe his brother. then because of his rage when he faced hanzo and accidentally killed yahiko, he didn't think it through, just wanted some power to killed hanzo and just summoned it. then he face the consequences by having those big rode things in his back crippling him. As we can see madara had something similar in his back in chapter 602.
It's just a thought/theory!!
It's just a thought/theory!!