You're welcome to your theory, but it serves no purpose to the current plot for several reasons. The Senju bros fought Izuna + Madara from childhood up until adulthood. They would both be as familiar w/Izuna's signature as their own chakra signature. This is the last year of the manga, and introducing any new elements in the form of a character is very pointless/unlikely. In a way Kishimoto is starting to tie up loose ends by bring Spiral to the field(who most of us believe to be Yamato). To simultaneously bring Kabuto back into the picture would make a lot of sense, especially considering the fact that Oro and Co. are b-lining to Sasuke. Oro may have stripped Kabuto of his snake-like properties, but he did not take away his intel, knowledge, and intelligence. If Kabuto did escape Izanami then he is as potent a threat as ever with or without Orochimaru's powers.