Madara when he 1st talked to Obi to he told him in order to awaken your full potential you must unlock your MS in both eyes.... so if Obi to had both of his eyes would he awaken Susano'o or something else? Because someone with Obitos ability to make people slip through him doesn't need susano'o. So he would awaken somethn else. Smart Kishi.... giving the slip through ability to an uchiha that has one eye.