For those who missed the last live letter, there will be two difficulties of the Criterion dungeon, normal and Savage.
This is the info they gave for Savage:
Note in particular there are time limits to kill things, meaning DPS will matter a great deal for smooth clears
This is from Balance, it's live translations of Yoshida's comments:
I reckon his comment that normal mode will be Savage difficulty might be hyperbole, but the Savage mode is certainly not going to be easy. Also, he mentions that gear from the raids will be important to clear, so it doesn't have its own progression system like PotD / HoH. So the balance we see in Savage will absolutely matter here.
If AoE opportunities are good then casters may get a look in, otherwise Melee/Melee or Melee/DNC are likely to be meta comps.