No races really came out of nowhere... Pandaren were first introduced with Chen Stormstout the Brewmaster as a bonus Hero in WC3. The Draenei have been a part of lore since WC3 in the form of the Broken and the Eredar. Blood Elves were in WC3, as well. Goblins were seen in WC2. And the Worgen were seen in Vanilla, albeit the feral ones and not the Gilneans.
I find it odd that Netherstorm is said to be alien when it's a zone in an alien world...
And Deathwing? Really? He's been in Warcraft lore longer than Arthas, Illidan, Kiljeaden, the naga, the old gods, etc.
And not to mention that Pandaren and Goblins were the two most DEMANDED races since WoW's creation.