Really, though, D&D could just shift a lot of the negative traits ascribed to goblins and orcs and whatever to certain low CR demons and make them more common as low-level enemies. It would also help give dretches and what not more personality.
Demons are pure evil without the civility that devils can have, don't reproduce, are invaders from the Abyss rather than natives of the world, and don't even really die when destroyed unless destroyed in the Abyss. Their presence in large numbers also increases the Abyss' link to a world, so wiping out incursions is also an imperative.