uh, I've been for a while thinking about a Nocturne Naruto, with a side-story of what if he denied the deal to become a demi-fiend and went for Devil Survivor instead. I've been planning this for a while so the merged universe wouldn't really make any universe overpower the other.
In my planned universe the Naruto world is a possible future of choosing the Chaos path on Shin Megami Tensei 2, and most bloodlines are the descendants of the mutants and human-demon couples that were able to live in the human plane on that ending.
But, about the personas...
In that universe, since it follows Megami Tensei, many humans have the ability of using magic naturally (actually besides the protagonists it's rare the ones that can't in the games), but the knowledge was lost since chakra was easier to use and control. The Personas, however, give them a huge boost in all abilities, plus dormant knowledge in the skills, magical or physical, they are inatelly better with. However, they are a risk due to being the manifestation of that person's Shadow, and trying to take control of them means facing your Shadow first (which is something hard to defeat by yourself) unless a contract with a being that can give this control is made - in the first persona game, the persona game is a ritual that allowed to make this with philemon. In If, instead of Personas you have Guardian Demons, they perform the same function basically. Personas are considered exclusive for beings originated from the human realm (I was going to say humans, but on Persona 3 there is a dog with a persona. Plus there's Persona 4's Teddie and the Anti-Shadow Weapons), since it is commonly said demons lack dual nature.
Well, as you see I've been thinking a lot about mixing the Naruto and Megami Tensei universes, even made a workshop for this "mixed universe" inspired by Daneel Rush' SayuMayu but I haven't been putting all my ideas in words there for some time...
Anyway, maybe we could talk later, discuss our worlds and share our ideas for the mixes?