I think people are way off about how Dark Rangers could be implemented in-game. I propose that Rogues get the Survival Hunter treatment and either Sub or Assassination is turned into a ranged Dark Ranger spec. Sure Dark Ranger abilities are part of the Hunter kit but Metamorphosis was once a Warlock ability too.
Problem 1: The Hunter theme is all about beasts and nature and is totally misaligned with the Dark Ranger theme. Dark Rangers don't have pets. Nathanos has his hounds but only in Vanilla and then very recently, but no other Dark Rangers have pets. MM Hunter is closest to High Elf Farstriders but even they are not the same as Dark Rangers. Sabotage and subterfuge is a big part of the Dark Ranger identity, which is spot-on if Dark Rangers were a Rogue spec.
Problem 2: Dark Rangers would look dumb as hell in Mail armour. There are very, very few sets that are going to be viable for Dark Ranger transmogs as a Hunter. Most of the gear is either covered in beasts or elemental magic because it's Shaman gear. It would suck to run around as a Dark Ranger but look like a Resto Shaman. Leather armour on the other hand, and basically all Rogue gear, is going to look great and consistent with the Dark Ranger theme.
But I don't think Dark Ranger is rich enough of a concept to be a whole class in and of itself.
Plus, as a Rogue spec, Dark Rangers would get stealth as a baseline, and it's hard to imagine Dark Rangers without stealth.