Complete speculation here, just an idea I thought was interesting.
Seeing as surv hunter is now a melee spec, and WoW definitely needs a new ranged DPS spec in the lineup.. Why not take the concept of Alleria and Sylvanas - two augmented huntresses who use either void/shadow magics, and implement it into a spec? Specifically, sub rogues.
Assassination has always had the "DoT spec" identity, and now Outlaw/Combat is, well. A pirate. But subtlety is.. What?
Subtlety has always lacked a concrete theme in WoW. The only thing core to it over the past few expansions was Shadow Dance, and even that is vague. What are you doing when you are shadow dancing? What is Nightblade? Infecting the target with a shadow disease..? Despite how fluid sub plays when not paying attention to what your spells are actually doing, I think this lack of a concrete theme is something they should address and perhaps work into a ranged weapon wielding, shadow magic augmented hunter. Perhaps implementing some themes from old survival hunter and mashing them with what sub is now?
Just a thought.