Very interesting you brought up taunka, which werent even mentioned in the article?

I think taunka are the "impure" that the article was talking about and the playable tauren are the "pure" ones. I say this because in dragonblight and eastern borean tundra, you can see ghosts of enraged taunka pathing around, and one who truly worships the earthmother wouldnt be left behind as a manifestation (in that matter). I've heard stories of tauren (and humans/nelfs) who's spirits appear in some great moment or to give world changing advice. (My favorite is when Terenas Menethil appears to tell Arthas "No king rules forever, my son.") But all these manefestations I've seen, none have been benevolent as the ghost taunka are.

Now that you mention it, I believe it has been stated that the taunka were more warlike than the "normal" tauren.
Also, and correct me if I'm wrong, I don't we've ever been told that the taunka believe in the Earthmother. Could the taunka be the corrupted ones? I mean they were pretty close to Yogg-Saron, atleast the Storm Peaks ones.

Another key difference is that the taunka coerce the elements into cooperation, rather than entreating them to, like the tauren do (for example, the elemental held imprisoned at Camp Winterhoof). This indicates (to me) a darker (less pure?) side to the taunka.

Or the Faceless Ones are the impure tauren, who listened to the whispers from below.