I'm the other No voter, and here's why:
Evil is a mind set. In order to truly be evil, you would have to sacrifice everything you once valued for the sake of something else. When Arthas went batshit DK evil and shit, the powers of the light forsook him and all that bullshit, but throughout the campaign, it was easy to see his deterioration from Paladin to jackass extraordinaire. He became evil, and thought of himself as such.
Draenei will never have the ability to become warlocks, unless Blizzard loses their minds, because they would be consorting with demons. I feel that the only way a spacegoat would qualify as evil would be for them to consort with demons, because, let's look at Draenor... oh wait, that's right.
Draenei DK is one of those race/class combinations that make as much sense as Gnome DKs. Yeah, people do them. Yeah, people RP as them, but how many of them are taken seriously in relation to how many of them are out there?