This is awesome, and I think it might end up being my head-canon too, because it makes so much more sense than anything canon has supplied. :)

It would also go a long way toward explaining how someone that potentially fucked in the head ended up coming out more or less functionally sane (at least for a shinobi) for someone of that generation, especially for someone who was promoted so young. A not-just-horrifying childhood would go a long way toward giving him ballast, so to speak. And the idea of him not being in the orphanage (and therefore not in Danzo's grasp) is something I hadn't considered before, but it really rings true.

Yay, head-canon.