I think we should keep The Faceless as a static entry in all predictions at this point .
Since Ash is the organizer we are guaranteed to have at least one more Sumerian band - likely After The Burial, BoO, Veil of Maya or Enfold Darkness - I guess Upon a Burning Body...not sure how they would fit.
I like the idea of Behemoth as headliner much more than DEP or CoB, they are great bands but just don't feel like Slaughter headlining material. They can fill most of the same venues (if not larger) on their own that SS plays. There are still plenty of other options for great death metal bands that I don't feel they need repeats yet. Off the top of my head: Atheist, Obituary, Carcass, Deicide, Bolt Thrower, Possessed, etc.