Originally Posted by
Tehr
If it's required that the only Death Knights are those that were around when the Scourge was blighting Azeroth, then I agree with all of those except Void Elves. Void Elves were not in the void fighting the Legion, they were Blood Elves who, very recently, were exiled from Silvermoon because they were studying void power. Just as the elves were mages, hunters, warriors, etc. beforehand, so too could they have been Death Knights.
However, my own suggestion as well as others simply say that Bolvar, Mograine, etc. can raise Death Knights, and do so after the events of the Broken Isles. There are TONS of sources of undeath in World of Warcraft, so why not allow DKs to play the new races?
The point is that they dramatically changed the lore of the world to allow for a specific race/class combo.