So, now it is known that the expansion will indeed feature those units. It's strange, but they once appeared in my dream, when they were storming some fortress, and their style was monotonously purple.
A few thoughts:
Units. As you can see, most factions have the same units. For example: Basic - 1 unit with physical attack, 1 ranged unit, 1 support unit (magical attack or attack and return). Elite - 1 elemental unit, 1 unit with physical attack, and 1 unit with magical attack (mage). Champion - there is a champion. Therefore:
Basic: Minotaur, Beholder, Beast.
Elite: Witch, Manticore, Shadow (elemental).
Champion: Faceless One.
But I feel sorry for the Hydra....
Their main specialty is, of course, increasing magical attack.