As Shadow Priest in WoD, you can have two specs in a one, if you go for a CoP, lvl 100 talent, like you play affliction and destro in one spec. You can DoT, if you need sustain or play dotless, if you need to burst someone down as quick as possible. As Affliction you have great sustain dmg, but you don't have any burst. Destruction have burst, but not enough sustain And Affliction DoTs looks really weak compared to Shadow DoTs: You need both; Haunt and DL up all the time, to do some dmg with them, while as a SP you can simply DoT up everything for the same result.
So, my question is: is it worth to stay a Destruction or/and Affliction Warlock for WoD PvP, if you can do everything better with SP? Don't know about Demonology ...
sorry for english ...