Blizzard's original warlock specs are more inclined to three different styles of the class as a demon summoner, which in fact is a system varying only on the extent of demon's participation in combat. In other words, the affliction warlock is merely a lesser demon summoner than demonological warlocks. In my opinion, that sounds like a controvercial identity of affliction warlocks regarding whether they are dark spell casters who can also summon demons or demon summoners who use weak demons (or a shadow priest who uses demons).
My suggestion is transmogging affliction to necromance by replacing demon minions with undead creatures. It doesn't feel odd that a warlock (dark caster) can control skeletons or ghouls. They can only operate in shadow, away from the public, and necromance has been extant in Warcraft prior to the founding of the Cult of the Damned, so the change would cause no contradiction to the basic plot.
The only issue is how to modify the existing skill mechanism... A more radical one is that two talent specs (necromance and demonology) would be enough for warlocks.