???
Draenei already have priests, and there’s no lore that conflicts with them being Shadow Priests. Lightforged Draenei don’t have Shadow Priests, but regular Draenei? There’s no lore opposing that.
And no, as long as Draenei hate demons (which will never change) you won’t get the warlock class. Demon Hunters are a maybe, because for the reasons I mentioned above, it doesn’t actually clash with the Draenei racial lore.
You really need to understand your lore better. Here, I’ll give you a lesson.
The Eredar, the species to which the Draenei and Man’ari belong, are as the lore states a race of extremely powerful arcane users, able to master all the forms of magic. When the Eredar were on Argus they outlawed the summoning of demons and the use of fel magic after Thal’kiel attempted to summon an army of demons which he was planning to use to overthrow Velen and Kil’jaeden, who were the leaders of the Eredar. Archimonde, who was Thal’kiel’s apprentice, rose to prominence because he aided Velen and Kil’jaeden in defeating his master.
Later when Sargeras was searching for powerful arcane wielders and tacticians to lead his newly formed Burning Legion, he found the Eredar and posed as a divine being, promising power to the leaders of the Eredar. Archimonde and Kil’jaeden were both eager to accept this power but Velen was not. He turned to the Naaru instead and when he learned the truth he fled Argus (the homeworld of the Eredar) with a not to insignificant number of others. Those that remained were either killed or willingly chose to accept Sargeras’s gift and become demons.
The ones who left called themselves Draenei, meaning ‘Exiled Ones’, the ones who transformed they called Man’ari, meaning ‘Unnatural Beings’. A select number of the Draenei would form a military force to hold the Burning Legion at bay for as long as they could. The Naaru would imbue them with power and they would become the Lightforged Draenei.
The Draenei attempted to resettle on multiple different worlds as they travelled through the great dark within the Genedar. Every time they attempted to settle they were discovered by Kil’jaeden’s forces and attacked, forced to flee to safety. This pattern of fleeing, attempting to set down roots only to be attacked by demons and be forced to flee continued for thousands of years, until the Genedar crash landed on a planet they’d call Draenor, which means ‘Exile’s Refuge’.
Kil’jaeden eventually found them again, but this time they could not flee. Rather than send demons after them directly though, Kil’jaeden instead used Gul’dan and Mannoroth to corrupt the Orcs, who at that time were at peace with the Draenei and some clans were actively trading with them. The resulting massacre paved the way for the First War to begin on Azeroth, and also literally paved a road called the ‘Path of Glory’ in Hellfire Penninsula. The road is literally made from the bones of slain Draenei.
When you pick the Eredar race in WoW, you are playing as a Draenei, not as an Man’ari Eredar. So, think hard for a moment about your experience as a Draenei. Demons have chased you from your homeworld, possibly slaughtering your kin who remained there, or maybe they turned into demons themselves. Then they chased you for thousands of years across the galaxy. They corrupt a race that is peaceful to yours and cause a massacre that results in the bones of your dead being used to make a road, then even after you escape Draenor, they still manage to follow you along with their Blood Elf servants to Azeroth and attempt to wipe you out there as well…
I shouldn’t have to spell this out, but for what I feel should be very obvious reasons, the Draenei HATE demons. They have no tolerance for them. And I honestly can’t blame them, because if I was a Draenei, hounded for thousands of years, learning that my kin had either been tortured, killed or converted into demons, I would not have any tolerance for demons either.
It’s that history that means Draenei will NEVER get warlocks as a class option. Man’ari Eredar can be warlocks, but Man’ari Eredar are not a playable race.