I agree you don't want unplayable demons in your deck, but the only demon I'd say for sure is unplayable is felguard.
Doomguard was considered unplayable.
I think succubi are iffey, losing a card isn't the worst thing in the world for warlock if you had to play her with the battlecry and she's big enough to get plenty value from the new card, sense demons could possibly fit into this deck and make up that card loss if you had to play her from hand. Felguard I don't see his unplayable status ever changing just because if you play him turn 3 you aren't really destroying one mana crystal you're destroying 7, or at least 1 + however many turns until the game ends before 10. Pit Lord, his battle cry is playable, although flame imp is better in the grand scheme of things and you can't take the hits from both flame imp and pit lord, that is why you never see pit lord, but pit lord may work granted you circumvent some of the battlecry damage from those two cards with the new card + you have sacrifical pact adding new life. Dread Infernal is absolutely playable, he just doesn't really fit into zoo or handlock.
I don't know if it'll work, but the new card at least brings the unused warlock cards into the equation.