I have a demon hunter idea, but it ties in a lot with my Emerald Dream Expansion idea (you can read the full version here
In creating my Demon Hunter, I took a similar approach to what was taken with Death Knight. Death Knights are a fusion of WC3 Death Knights, Necromancers, and Runemasters. My Demon Hunters are a fusion between WC3 Demon Hunters, Wardens, and Druids of the Nightmare.
For my idea, the demon hunters start in the Ravine of Shadows, an Area of the Emerald Nightmare south of the Eye of Ysera. The player character is an Unwaking, trapped in the Nightmare. Here, they find an unlikely ally; Illidan Stormrage, his spirit more specifically.
"But HED, he went insane!"
you say? I have a way to explain that. One name; Gul'dan.
Basically, Illidan didn't just get Gul'dan's memories when he absorbed his Skull; in fact, Gul'dan's spirit possessed him. When Illidan was defeated at the foot of the Frozen Throne, Gul'dan took control. Illidan became a prisoner in his own body as he watched Gul'dan pose as him, oppressing Outland. During the raid on Black Temple, Illidan embraced death, seeing that it would free him from his imprisonment. But Illidan was not content with dying; his spirit found its way to the Emerald Nightmare, where he became trapped again.
But this time there was a way out of the prison. Instead of resisting the energies of the Nightmare, Illidan embraced them, bending them to his will. Illidan freed himself, but he had no body, and all the people of Azeroth saw him as a monster. And so he remained. He began training a new order of demon hunters from those who had become Unwaking.
The final part of the starting zone has you, Illidan, and various other demon hunters save the day at the Eye of Ysera, defeating an attack by the forces on the Nightmare. After Eranikus was purified, the Old God behind the Nightmare revealed himself and now seeks to corrupt Ysera as its champion. However, the Old God will find that the Nightmare will not be its for long.