The following was just data-mined on wowhead/mmo:
NEW Stage 6: Confronting the Margrave
Confront Margrave Sin'dane about Kel'Thuzad's treachery.
NEW Stage 7: The Third Fall of Kel'Thuzad
End Kel'Thuzad's manipulations in Maldraxxus
What kind of role do you think he will be playing? Do you think he's going to attempt to take control of Maldraxus? Who is he working for?
Mod Edit: Repurposed this thread to discuss returning NPC's in general.