At one point at least one mag talked about an attempt to do a 3D Bonk game. It was back during the 32-bit generation and I believe pre-N64. I remember my impression from what I read. 3D platformers were still pretty crude and developers were still figuring out how to do traditional genres in 3D. If the story was legit (probably EGM... probably Quarterman), then Ultra Genjin was probably just Bonk 3D. Since the biggest hurdle would have been trying to incorporate the spinning, it would make sense that they'd come to a point where they said "screw it! Let's just make it a Bomberman game". If things had gone smoother, then it likely would have come out sooner as Bonk 3D on Saturn. Bomberman was the dumping ground for Hudson's experiments back then (Bomberman Fight, Bomberman Wars, etc).
I deffinitely recall talk of a Bonk 3D game for PS1. So, I don't know if it was the same as Ultra Genjin or not.