I'm glad I'm not the only one who believes this theory. I have thought this for a long time, but never bothered to make a case for it. All the points made in your post just make me even more sure that this theory is true.
But why haven't we found out before now? Revealing this background story seems like something that would happen right before Tsunade's death. Just like we are getting Kabuto's whole life story right now. True, Tsunade is alive and well, for now, but for how much longer?
Nice post. In any case, we will find out soon enough if this is true.