I have so given up trying to predict the end of DN. I'm wondering if there's going to be any moralism at all; hell, maybe there will be a non-ending and there will be eternal conflict between Light and L. Personally, I'm inclined to think #1, and that Light has never been insane, and that the DN makes people, instead of supernaturally evil, supernaturally free.

IMHO, L wouldn't use the DN. He'd like to, actually, just to see how it works, but it's against his rules. However, it's not as if L's rules are the same as society's rules. L sees himself as above the rules on certain matters.