Demon Hunters as we know them, are now essentially a Warlock Hero Class. As Ghostcrawler said, "Is there anything Demon Hunters will add?..."
And in addition to that, Hunters are only class in the game with an exclusive weapon set. No other class has that. The next class added to the game will take advantage of ranged weapons, I guarantee it.
Demon Hunters are added as a distinct individual class, I predict at least one spec taking advantage of ranged weapons. I predict that it will be the spec to explain, in canon, why races like the Draenei, Tauren, Pandaren, and Orcs (assuming they have some anti-demon dignity left after MOP) are able to play as one. It will be the spec that says "We don't merge our souls with a demon, but we will dedicate our lives to eradicating them."
It gives the Marksman/Petless Hunter argument a rest, as well as the demon hunter argument. Is it canon? No. But neither are our current version of Warlocks, priests, and death knights. Blizzard will add the lore to fill in the blanks.