I heard about this a couple days ago, then I actually saw it in Marvel Previews. We already have the Dark Avengers, now we're getting the Dark X-Men, and honestly it looks pretty cool. The roster is very random, but thats partly what makes this book very interesting.
Namor
Emma Frost
Mimic
Cloak
Daggar
Daken
Weapon X? Is this supposed to be Michael Pointer AKA The Gaurdian
Dark Beast
Many of these characters have not been used in quite some time, and if used its been sparingly. We still get A-listers and regularly used in Namor, Emma, and Daken. I'm the most excited about Mimic, I've wanted Marvel to dust him off and use him already, and they finally are. Cloak & Daggar has been used here and there in Runaways, New Avengers, Civil War, but not much has actually been done with them. Dark beast was last seen shortly before Messiah Complex and Excalibur way back before House of M. If Weapon X is Michael Pointer, then I think Dark X-Men is a way better fit for him then Flight, plus if he is Weapon X, then that frees up the Gaurdian Identity for Flight. Emma and Namor are in the Cabal together, and like Wolverine Daken has to be in multiple titles, joking aside he's a perfect fit. One last interesting observation, many of these characters are "questionable mutants"; Namor, Mimic, Cloak & Daggar.