People need to think logically. Now I'm not going to say that it's confirmed either way, because it's not. It's all just speculation. However, all of the evidence is starting to pile up in favor of the new races.
1. The speculated "Maelstrom: Cataclysm" expansion. This would include Undermine, which would be a great starting place for the Goblin.
2. Blizzard's harsh action against the Worgen pet. First they decided to remove it from all pet families to make it no where near viable for raid dps, then they just reverted it back to a white wolf. You could argue that it's because Blizzard didn't want a humanoid pet, however, but it just doesn't seem that way to me (i.e. ghost wolf pet).
3. Completely new texture for worgen mask. They updated worgen models and textures for wotlk. Why would they make a whole new texture for just some silly halloween mask?
My brain is in a bit of a fog right now so I can't think of anything else, so those are just a few examples.
If it really does turn out that they are new races I believe the Horde would get Goblins, and the Alliance would get Worgen. Why?
Horde has been paying Goblins for a long time for Zeppelins, while Alliance ENSLAVED a goblin for forced transport to Northrend.
Worgen lolore: Archmage Arugal brought Worgen to this world as a last defense for Dalaran (yeah, he was a Dalaran Wizard) against the Scourge. However, the Worgen killed people as well as scourge, causing Arugal to exile himself being too embarassed. Maybe Arugal commands the Worgen to be "mercenary's" for the Alliance or something as a change of heart?