The craze for selecting class hall sites began with the Shamans of the Maelstrom region, then swept across the entire world, prompting every class to follow suit.
In Outland, the Illidari announced that their class hall and holy ground would be established in the Black Temple of Shadowmoon Valley. They also possessed a mobile class fortress: The Fel Hammer.
After the Empire had completed its research and reverse engineering of the Fel warship, this trophy—once brought back by elite Demon Hunters after their raid on Madness of Shattered Depths—was returned to them and now hovered directly above the Black Temple.
This was a Burning Legion main battle warship, so its interior was not as spacious as that of a transport vessel. However, there were never that many elite Demon Hunters to begin with. While there were quite a few Demon Hunter apprentices in training, they were not yet qualified to board this aerial fortress. Thus, the Illidari designated The Fel Hammer as a mobile aerial fortress for their elite forces.
At the same time, the Illidari issued an open recruitment notice to the Night Elves and High Elves, welcoming any elves who wished to become Demon Hunters to train at the Black Temple and join the ever-growing ranks of apprentices. Chief Instructor Illidan Stormrage would provide them with unified instruction.
Illidan was living the good life in Outland. Whenever he got bored, he could kill some Fel beasts for entertainment, or fool around with Maiev Shadowsong. He would not trade this leisurely, free position as an empowered feudal lord beyond the Empire for anything.
Back to the point: the Illidari had a rather mixed membership. Besides the elven Demon Hunters who formed their elite backbone, there were also Maiev's Watchers, Akama's Broken, and the Fel Orc tribes.
Oh, of course,