Many fans are anticipating Goblins to become a playable race in World of Warcraft Expansion.  A comment by Fangthooth, however, suggests that i might not be so:

” Goblins, while being very cool, are in it for the Gold. If they chose either the Horde or Alliance, they would lose out on 50% of their profits. It is better for them to stay neutral and make more money, than choosing a side and slaying potential customers”

Of course, we are listening to this from a Murloc, ahem.  If Goblins ever made it to be a playable race, I imagine it would be a new faction that plans to dethrone the Princes of Trade or one of the Prince of Trades seeking to purify Undermine of the evil and black markets threatening his nation.  The Goblin Princes of Trade are very powerful, each with their own army and trade outposts.  Some delve into black market, and many goblins are known to have joined the Shadow Council and Twilight Hammer Sects.