"Not work safe" covers a much wider territory than NC-17, though.

That could be either a bug or a feature, and I'm not sure which. On the one hand, ratings are sort of like spoilers (although less so than warnings); on the other hand, they are fairly useful in deciding whether to read fic or not.

But yes, if we want to keep the rating structure basically the same while avoiding the implication that the purpose is to protect children from the truth about their own bodies, "Explicit" could be a good choice.