I've read most of the theory (sorry it's not all), but I have to agree with a lot of what you said. Though I've heard a lot of theories like this, all or at least most having a girl from the Hyuuga Clan marry (mate/whatever) a none human. Thus making an Uchiha.
But one thing I don't understand, is when there's only one Hyuuga, most theories never say that there's more. But only one (girl, usually) Hyuuga that goes with a none human, and they have children. Then what do the children do? Do they have to marry their bother/siste to make pure Uchiha's or marry outside the family?
I personally don't like 'inside the family' stuff. But i've always been curious in how anyone come's up with a 'pure' Uchiha, if there even is one.