There are an awful lot of loose threads around the tauren right now. The Grimtotem are scattered, making temporary pacts with the Alliance in Stonetalon, besieging the night elves in Feralas, and their greatest leader was last seen claiming an artifact of elemental power. In the wake of Cairne's death, Baine Bloodhoof chose to allow Garrosh to rule uncontested - but that position clearly changed over time, and Baine led tauren troops to the support of Vol'jin's rebellion against the Warchief, rather than simply challenging him as his father did. Ironically, this choice shows a certain political maturity - recognizing that trial by personal combat might not be the best means to effect regime change in the Horde - while it also shows a bit of a break with the old ways of both the Horde, and the tauren people.
Baine's father Cairne chose to live, and die, by the older ways of ritual and honor. Betrayed by Magatha, he died from poison on Garrosh Hellscream's axe and with him seems to have died the last vestiges of the tauren ways of the past. Baine led an expulsion of those Grimtotem that would not swear allegiance to him over Magatha that culminated in a battle against their last leaders in Mulgore, and at the end of that battle, Baine ruled the shu'halo as undisputed chieftain of all. But in doing so, he also led his people into their last break with the past, and following the defeat of Garrosh and the ascension of Vol'jin to the seat of power as Warchief, one must ask - what role do the tauren fill in the Horde to come, and where will Baine's current choices lead them in the future?
Right now, the tauren are basically divided into two camps. One, the majority of the tauren people, are united more or less underneath Baine's leadership. We saw some tensions during Baine's leader short story - some tribes like the Farwanderers wanted to resume a nomadic way of life. Baine's eyes were fixed on the Horde as something his father had helped create and shape - his father, alongside Thrall and Vol'jin had laid the foundation for the races that did battle against Archimonde and the Burning Legion atop Mount Hyjal, and the Horde as Thrall had come to rule and define it. As long as Thrall had been Warchief, Cairne's advice and wisdom had been respected and heeded, and Baine didn't wish to abandon it. When dealing with the quillboars, he'd attempted to negotiate, but they were uninterested in such a debate. Eventually Baine had to rescue Garrosh from them, when the Warchief refused to listen to his advice.
How often, when standing outside the gates of Orgrimmar with Vol'jin during the rebellion, did Baine regret his actions then? It's interesting that on the face of it, Baine very much intends to maintain his father's principles and his father's ideals regarding the Horde, and his support for Vol'jin may have had as much to do with that desire as any personal friendship with the troll leader - but it's also clear that Baine and Vol'jin formed a fairly close alliance during the Theramore attack and Pandaria campaign, and that the two both share many qualities. Both are the sons of fathers who left a big impact on their people and a huge legacy to overcome, and both were marginalized and abused under Warchief Garrosh Hellscream.
But now that Hellscream has fallen, what is to be the role the tauren play in Vol'jin's Horde? Will Baine fill the same sort of advisory role that Cairne did? Carine, although still physically powerful (strong enough that he could reasonably expect to defeat Garrosh in hand to hand combat, and Garrosh himself saw honor in a fight against him) was an aged tauren, old and past the part of his life when he could reasonably expect to engage in hunting or combat regularly. Baine, on the other hand, is a much younger shu'halo than his father. He may not be satisfied with an advisory role.
Furthermore, Baine has a far more open enmity within his own people than Cairne did, and in the wake of Hellscream's fall, it can be truly said that Magatha Grimtotem is Baine's greatest enemy, and one of the greatest enemies of the Horde. As seen during Cataclysm, the Grimtotems harbor the ambition of ruling over all tauren, over Mulgore, and over Thunder Bluff, and it is unlikely she'd be able to do so and remain at peace with the Horde. With Vol'jin as Warchief, any attempt to come to power would have to deal with him as well as Baine. At present, Magatha is the greatest wild card in terms of Horde relations with the tauren as well as tauren as a whole relating to each other. Much like Maiev Shadowsong, Magatha is a traditionalist who sees alliance with other races as a weakness, and her Grimtotem tribe reflects these prejudices, but it also reflects her unique pragmatism. For a racist, Magatha was fully willing to work with the forsaken to achieve her aims, and her Grimtotem made common cause with the Alliance while simultaneously attacking them elsewhere.
It would be interesting to see if Magatha can make use of the fraying edges of the tauren people and their discontent with the Horde following Garrosh's downfall, or if his having taken part in the rebellion has elevated Baine's standing in the eyes of those of his people who were feeling exploited by the Horde under Hellscream.
Another element of the tauren presence in Mists of Pandaria to consider is the expedition to Pandaria led by Sunwalker Dezco and the role of his child in the future. While one of Dezco's calves died, the other was surrendered into the keeping of the Golden Lotus, apparently to serve some greater destiny. But this leaves Dezco and his expedition, initially sent by Baine (because all tauren had the visions that led Leza to lead the expedition to find Pandaria before the mists had even parted) to discover this lost land. Now, we already covered a load of speculation about the waters of the Vale of Eternal Blossoms and why Chi-Ji wanted Dezco's child, but instead, let us consider that as of right now, the tauren are the only Horde race with a solid connection to the future of Pandaria and a race of cousins who have been trapped between the pandaren and mantid for ten thousand years. The contact between tauren and taunka in Northrend led to taunka joining the Horde, and in some way may have inspired Garrosh Hellscream's True Horde and its Dark Shaman to attempt to take power from the elements.
Will the tauren and the yaungol come to a similar connection? Is Dezco's child destined to lead the Golden Lotus to a new understanding with these distant kinfolk? In time, will the yaungol join the Horde? It's unknown yet, but right now thanks to Dezco's expedition the tauren are as close as they've ever been to reuniting all the disparate branches of their people in some form or another, even if only diplomatically. And if Baine can somehow manage that, it could have further reaching ramifications than anything the tauren have ever seen.
The tauren have never been a race of conquerors, or a force to dominate the world. But Baine has begun the subtle process of changing how his people view that world. What the future holds could well be a world ruled by an iron hoof.