The idea of a Terminator vs. Predator story is not stupid at all. I think it's a really cool concept.
In my opinion, I think it would just work as a comic book/graphic novel or just a paperback novel. I have thought about writing a Terminator vs. Predator fan-fiction story. No, I will not use the Arnold character, but I think a Terminator vs. Predator story could be interesting.