Velen was a seed, the start of something much larger. For the naaru knew that in order to fully defeat the Burning Legion, they would have to spread this awareness of the Light that they'd been carefully cultivating until it shone brightly enough to defeat any darkness that dared to threaten it. They spoke of this to Velen and the draenei, telling them that there were other forces in the cosmos that would stand against the Burning Legion as well. The Titans that roamed the universe, placing order and creation where there was none, were a good start, but the naaru would have to recruit many, many more followers into their fold in order to create the kind of pure connection required between universe and self that would defeat the Burning Legion.
In the end, the two parted ways, agreeing to simply work each in their own way to the best of their abilities. After all, what mattered was the message of the Light, the peace it would bring and the defeat of the Burning Legion. E'lune soon found herself attracted to a strange pool of water that pulsed with the magic of the arcane and nature, the apparent source of the world's magic and power. This would be an excellent place to focus her efforts and cultivate a race that would be just as powerful as the draenei. And so E'lune sent out a call, a soft song of peace and the Light, and waited.
In gratitude, E'lune granted them an "improved" form -- lengthened their bodies, straightened their backs and gave them the power of the Light to heal and protect their brethren. The eyes of the trolls -- now night elves -- shone with the brilliant reflection of the blessed Light of E'lune. The night elves prospered, and E'lune continued to watch over both them and the strange Well of Eternity that fueled the natural magic of the world.
In time, E'lune observed Malorne, a powerful creature native to Azeroth that watched over and cultivated the natural magic of the world in ways beyond her comprehension. To this demigod she also spoke, but Malorne was unwilling to change himself, as he was intertwined with the world in ways E'lune could not understand. Instead, he created Cenarius, an offspring who was just as connected with the earth and nature as he himself was, in an effort to help the cause of E'lune in what little way he could. E'lune granted Cenarius the same powers that the night elves now possessed, and Cenarius evolved into a being that was part nature, part Light, and used the two powers seamlessly in what we recognize as the druidic powers of present day.
E'lune was horrified but continued to teach those of her children who would still listen and work her powers of persuasion on the other creatures of Azeroth.
Meanwhile, An'she had settled on the other side of the world to observe. He observed E'lune's activities, he observed the Sundering, he observed the natural races of the world and the best ways to reach out to them. He watched the earthen, felt their pain at the rending of the world and their deep connection to it, and watched as they hid themselves away and hibernated, all the while growing softer, weaker. And he watched the vrykul of the north and their strange, smaller children that were abruptly tossed out and forced to fend on their own. Shunned by their people, in much the same way as the draenei ... And one day, An'she finished observing and began to act.
But some creatures had been forgotten -- the tauren, a race that had been there since the dawn of time. The tauren knew that E'lune and An'she existed. The world they were so deeply connected to was changing as a result. They knew of E'lune, or Mu'sha, through Cenarius, who sought out the tauren and taught them a little about natural magic before turning his full attention to the night elves created by his mother. The tauren learned of the ways of Cenarius, who had been granted half his powers by E'lune. But the little race of nomads had yet to realize their full potential, though they knew something was ... lacking.
Unfortunately, we've been given very little information so far to confirm this one way or another, but there are many different ways that tauren paladins and priests could naturally fit in, given existing lore and the holes within that lore that have yet to be explained. This is my theory: it's all the naaru. Every last bit of it. What's your "Tin Foil Hat" theory? Got a different explanation that could make perfect sense? Leave a note in the comments, as discussion is always encouraged in lore speculation -- and come back next week when I tackle the Alliance side of politics and where they're headed come Cataclysm.