Pedophilia... for a fic, not art, involving a chibi form. (Is the chibi form canon?) Gaah.
Yeah, the chibi form was canon, and it did look pretty childlike. I think the idea's a bit squicky, but jeez, nobody was forced to read it. I only heard about it secondhand, so I don't know whether the story had proper warnings and whether that might have helped.
And you're right, it's really hard to figure out how to label the warnings sometimes. I do like your idea about warning for general squick and having a whited-out qualifier for those who don't mind being spoiled. For sex and violence it may be a little easier for the organizers to come up with detailed ratings guidelines. Fiction Alley actually has a pretty well-defined system, although it is rather restrictive, since they have a lot of underage fans using the archive. For those who tend to over-warn, it might help to know what levels of sex and violence are acceptable for each rating.