If Tobi can be Obito, if Madara could be a Rinnegan user, if Kurama can turn good, if Sasuke can appear overall irrelevant to Obito's plans and if Orochimaru can return through the most bizarre means... Clearly nothing is impossible in this manga. So yes there is a chance that there might be a being above the Rikudou Sennin and the Juubi.