This is my prediction for SL... the big twist. Not much to base this on other than my gut feeling. Plus we already know the Arbiter determines where souls go when they die, so what if she's the one dumping them all into the Maw? She's just convinced everyone it's this mysterious Jailer who is actually opposing and trying to stop her. He attacks us in the Maw because he sees us as her agents.
Unfortunately, this would mean Sylvanas is good too.
Edit: Oh, I also think the Jailer is the smith who forged Frostmourn/Helm of Domination...