Everyone knows for a fact that the SO6P is the daddy of both the senju and the Uchina, correct?
Well I'm also guessing that none of you thought of something very obvious.
If a Senju desendant married a Uchina their offspring would be of the SO6P caliber. He would have an Uchina Sharingan and Senju Body, So he/she would be awesome.
How come nobody thought of this?
Mainly because to be strong isn't something you can aquire through nature; one of the characteristics of a strong Senju bloodline is the mental determination and physical longevity. However, this state of mind isn't something that can be "passed down", it is God-given. To never give up in the face of adversity and to believe in what is right, and not be corrupted by power cannot be taught, it is a birthright.
Basically to create a "SO6P", we need a Nagato & Uchiha combination, along with the traits that Naruto has, and that is INSANELY UNLIKELY, as proven in the series, as Naruto is the only one with pure ambitions, while Nagato and Sasuke became corrupted, Nagato re-inspired himself, but Sasuke plunges deeper into the ocean of darkness.
But despite this, if such a combination came to light, that Shinobi would most likely be insanely powerful. The reason why no-one "thought of" , or "attempted", is because the Senju and the Uchiha were mutual enemies, with big differences, it would take a Gorbachev figure in both clans to make such an event come to light.