You attacked Thimagryn for "ignoring lore", yet you seem to disregard recent warlock lore, and the shape the class story has taken. DH lore is limited and old, but Warlock lore is recent and specific. It's demonstrable in game that warlocks are not pursing melee combat, and are not wholly focused on demonic magic. Even Kanrethad, the ultimate demo lock, had a powerful new destruction spell inspired by Deathwing: Cataclysm.
The warlock class is not going down a melee road. Dark Apotheosis was hardened survival stance, not a melee combatant. (One I am very sad to lose next expansion). In fact, we look to be learning from Kanrethad's warlock superiority in the next expansion with
Cataclysm and
Demonic Servitude as level 100 talents. Not at all things I'd expect from a DH.
We only have a little lore and mechanical inspiration to work from regarding Demon Hunters. It's the reason why so many of us are so willing and able to extrapolate from what is to what could be.
This is WoW, it's supposed to be a world of unlimited possibilities. Nothing should be considered absolutely impossible. Blizz has expressed interest in bringing Illidan back some day. That could be a great launching pad for a DH class (whether Illidan is the player's class leader, or nemesis again, is entirely open to discussion).