When I was in like 5th grade, I gave a guy an idea for something like that and he made the site for me. It wasn't successful, but it would have combined several DBZ rpgs, including mine. The way we did it was that on the new site, everyone would remake their character and that site would have its own, simpler system.
This was way easier with dbz because there weren't any real attacks. It was the same energy blast with a different name. I think it could work with Naruto, but like I suggested before, we could have Jiyuu characters do it individually and not transfer the stats back to Jiyuu. And also Jiyuu wouldn't be officially affiliated. That would be my way of going about it. What do the mods think?