I honestly dont think draenai warlocks are out of the realms of possiblity
Dont forget there brothers the eradar embraced fel magic and if the next xpac is set on argus they could reunite and reconcile with some of there eradar brothers and allow them back into the fold and forgive them though it would mean you could only play as a red draenai which would be badass.
If thrall could forgive warlocks im sure valen could too
Anyway i think lorewise i would have to say pandaren deathknights seeing that there is no way pandaren was around to be raised into a deathknight.