Spooncraft

We still don’t know the nitty gritty details but one thing that seems pretty much legit would be that your account must have one high level character in order to make a Death Knight. This makes sense in many ways as the Death Knight isn’t supposed to exactly be super powerful, just something special that seems more epic than most of the original starting classes. Reading more into the thread Blizzard also has no plans on making race restrictions to the new Hero class. This I kind of disagree with. Even the first death knights ever created were Orc souls placed into dead corpses of Stormwind soldiers when the Horde burned the city down during the 1st war. As well in Warcraft 3 the Death Knights are all humans/human like creatures.

The two major Death Knights in the game lore (Terron Gorefiend the first Death Knight and Arthas Menethil) are also in human form.

You will still need to have a character on your account of the appropriate level to even be able to make a deathknight. (src)

But hey… you know… Gnome Death Knights… yay…