this made me wonder... according to tobi/madara the senju and uchiha were born from Rikudo Sennin and his powers were split between them. so in essence they are 2 parts of 1 whole. tobi/madara has been waiting for sasuke to fully awaken his sharingan, which was the gift to the uchiha from rikudo. maybe tobi/madara hasn't taken naruto because he's waiting for the gift of "body" from rikudo to be fully realized by the senju descendant (if naruto is really a descendant) so he can put the 2 together again, in his own body and become like rikudo. then he could host the 10 tails, JUST like rikudo. madara wants all of rikudo's legendary power, not just the half his descendants were given, but the "body" that was given to the senju too. tobi/madara has also mentioned that he wants to be complete. i don't know, just thought i'd throw it out there.