I don´t understand that. In the WoD ending cinematic, Archimonde is saying to Gul´Dan: "We have a Pact.". And why Sargeras has a pact now? And with who? With Archimonde or Gul´Dan? I think that this turnes out to be that Archimonde and Sargeras had a Pact to summon the Burning Legion to Draenor with the goal to stop Grommash, Yrel, Khadgar and us and that Gul´Dan is responsible for this mission. The second possiblity is that Sargeras is coming to Azeroth after Archimonde failed (again), but this is not fitting in an expansion with Azshara at all.
A Jailor is a keeper of something. Maybe it is referring to Tyr who is keeping that what is under Tirisfal and who is now awakening.
I think that this is referring to "the next step" with the Burning Legion. Is the Legion finally coming to Azeroth? Maybe.
Wouldn't be surprised if demon hunter is just the name of one of the new class' specs