Each set seems to have a specific inspiration
Warlock - Ner'zhul
Rogue - Giest
Priest - Cultist/Acolyte(Cult of the Damned)
Paladin - Lavaman/Bolvar
Mage - San'layn
Death Knight - Arthas
Hunter - Anub'arak/Crypt Lord
Druid - Nightmare/Valithiria Dreamwalker (if Nightmare, then its not really connected to Scourge)
Warrior - Boar (not really connected to Scourge)
Shaman - Remains to be seen (I'm hoping for Frostwyrm/Emberwyrm inspiration personally)
Personally, the color in the picture for Priest makes it look generic. I'm hoping the others are more Cultist-y