It was confirmed at the Fest that there's one more Battletome per GA this year.
What is not confirmed is:
If it is ONLY one per GA or min per GA.
And if the one for Order includes Slvaneth (unless I missed something)... so there may only be three more announcements this year.
My guess:
Order - Sylvaneth. If not including Sylvaneth, then Kharadron Overlords
Chaos - Slaves to Darkness, Everchosen, Darkoath soup.
Destruction - Ironjawz
Death - not sure about this one... Death Rattle or Soulblight...