All i got from them (which you can see on Patricks page) is that they want it to be a surprise when they announce the class roster.
I remember in the Night Lords series, one of the Raptors was this stalker psychopath, with sonic-vision, that would crawl on walls and through ducts to hunt down enemies of the warband, taking skulls and, occasionally, skin pelts. So.... Raptor...
I REALLY hope we can crawl along walls. The fluff describes raptors as all being like this where they prefer to crawl like beasts.
Considering that they said chapter specific things like Wolf Priests will be ingame i wouldnt rule out the Dark Apostles as a hero option.