In last week's Patch 10.0.7 PTR build, hints towards a questline involving Baine Bloodhoof have been found in datamining. In this week's build, although the questline is not yet testable, a couple more hints have been found! The first new hint for Baine's questline is the possible name of the questline: Old Hatreds.
NEW Old Hatreds Mayla Highmountain is worried about Baine, who has travelled alone to the Ohn'ahran Plains in search of a missing friend. Seek out Mayla in Valdrakken to learn more.This questline name is a tie-in with the fact that the Tauren do harbor hatred towards the Centaur race as a whole, as they believe the Centaur are a curse brought upon them by forgetting the ways of the druidism in the past, and the reason why the Tauren became a nomadic race for the longest time. This is explained with the in-game lore book Hatred of the Centaur.
As the mists of dawn faded and the Age of Memory advanced, the demigod, Cenarius, went his own way through the fields of the world. The Shu'halo (tauren) were sorrowful at his passing and forgot much of the druidism he had taught them. As the generations passed, they forgot how to speak with the trees and the wild things of the land. The dark whispers from the deeps of the world drifted up to their ears once again. Though the children of the earth closed out the evil whisperings, a terrible curse befell their roaming tribes. Out of the black lands of the west came a horde of murderous creatures — the centaur. Cannibals and ravagers, the centaur fell upon the Shu'halo like a plague. Though the braves and hunters fought with the Earthmother's blessing in their hearts, the centaur could not be defeated. The Shu'halo were forced to leave their ancestral holdings behind, Read more on wowhead.com