"Records indicate that the worgen existed for a time in Kalimdor. In fact, more recent evidence suggests that their true origin might have a connection to the night elves and a secretive druidic order from Kalimdor's distant past. Yet until new evidence comes to light, this information remains speculative." -World of Warcraft: Cataclysm Official Site
Worgen Druids? Wolf Totems?
Druid lore currently states that the night elves honor a specific animal totem in order to gain the ability to transform into that form. Originally, a druid chose a specific animal totem and was categorized by that type. Druids of the Claw honored the bear spirit, Druids of the Talon honored the stormcrow spirit, Druids of the Fang honored the snake spirit, and Druids of the Antler honored the white stag, otherwise known as Malorne, who is now unfortunately perhaps little more than a spirit.
Modern times have forced the druids to evolve their methods and teachings, and now druids are permitted to study multiple animal totems. These Druids of the Wild (named so from the tabletop RPG supplement) can shapeshift into any creature whose spirit the druid has properly honored. Druids in World of Warcraft are patterned after the Druids of the Wild, who have only come about largely since the end of the Third War.
How many animal totems are there? Well, we don't actually know. Consider, for example, that the original classifications only include Druids of the Claw and Druids of the Talon (bear and stormcrow, respectively), but World of Warcraft expanded that to include Druids of the Fang and Druids of the Antler, (snake and white stag). Then consider that the player-controlled druids also have the capability to shift into a feline, and you start to see that the animal totems aren't necessarily dictated by public history.
So why not a wolf or worg totem spirit? Wolves, per traditional real world lore, are generally tied to the moon, and night elves worship the moon goddess, Elune. There are wolves across the various regions of Kalimdor, too. So why shouldn't it be possible for a "Druid of the Paw" (yes, that's a joke) to exist?
Of course, you can take one look at worgen and a shapeshifted night elf and see one major distinct difference: druids shift almost completely into their animal totem's form, with only a vestigial hint at the core race (horns for tauren and elongated ears for night elves). Worgen, conversely, seem to be stuck into a hybrid form. Granted, there is a quest in the Grizzly Hills where we see a worg shift into a worgen, so a full animal transformation is not out of the question.
So the question remains: What are they? Are they night elves half transformed into wolves / worgs? Are they a new species entirely, created as a weapon by the aforementioned secret druid sect to fight against the Burning Legion? How are they tied to Elune and the Scythe? Are they REALLY tied to Elune at the source, or is their connection to Elune artificial?
If the worgen truly are connected to some lost or as-of-yet discovered wolf totem spirit, then what other totems are out there that we have yet to see?