A lot of people are upset about draenei and lightforged draenei warlocks. However, with proper writing, these can make sense. But it would be a major event. Let me explain:
A few years ago, we defeated the Legion. Argus was destroyed, severely slowing down the process through which demons are reborn in the Twisting Nether. Sargeras, the one thing keeping the Legion together and enabling the Burning Crusade, has been sealed away with the rest of the Pantheon and Illidan. But the Eredar are still there. Leaderless. Both Kil’jaeden and Archimonde are gone and their one purpose has been taken away from them. So, who do they turn to? The one person who would welcome them back. Who would forgive them.
Velen.
And he does. Despite everything, despite all the evil, the pain, the death, Velen welcomes them back. Some even decide to prove their loyalty by becoming lightforged. And if you think that makes no sense, you don’t understand how the forces of the Warcraft universe works. Disorder isn’t the Light’s antithesis, Shadow is. The Light will gladly take fel beings into its fold. Remember what Xe’ra tried to do to Illidan? And we can see it through Lightforged mages wielding arcane magic, as an example.
But this shouldn’t sit well with the rest of Azeroth. People never really accepted the death knights who freed themselves from the Lich King. Now imagine Eredar. In fact, I’m fairly certain a lot of people in the Horde would start losing their minds at the Alliance consorting with Eredar. It could be a very interesting plot development.
But that’s how it needs to be done. Don’t just make it a pickable class. Give us playable Eredar. Give us new draenei and lightforged draenei customizations for them. Give us some plot developments. Then it works.