I'm not sure we really even need a book of this sort.
Even the people who want to explore these themes - they don't need game rules for it. I'm sure there are other, better sources, that can be adopted into roleplay that takes place at the table, with the clothes on, rather than other parts of the house per se...
Vile Darkness failed for me because it was well, not an exploration of evil in roleplay, but of comic book villains. It was about as dark as the X-Men during the Goblin Queen run of the late 80s...
I get better source material for evil plots by watching Law and Order, opening a newspaper, or listening to what goes on in the courthouse... I'd take things from the real source material, and use the Law and Order method to 'tone it down / filter it' for people not used to being exposed to that kind of worldview. (that said, there's nothing like sitting a set of players who like horror and gangster movies down to a session with a villain who's modeled off of the mindset of a real world pimp / dealer - now that's dark and mature content. But don't expect them to be willing to return.)
But I'm digressing.
I guess I don't see the need for gaming books on these subjects. If you want to do horror and gore, do it, but don't get pretentious and pretend its anything more mature than the X-Men. And if your desired subject is kink - recognise that your book is mostly going to sell to people that want a laugh at it, and that people who actually plan to use that kind of content in game have better source material.