Can't find it right now. It was some interview during Cataclysm. If I find it I'll post the link. I think the reasoning behind it was that Gilneans didn't have a good standing with the Alliance, and their land was close to the Forsaken. Goblins can be put anywhere, as for them it's all about the money anyway. There's rivalry between the Goblins and the Gnomes but so is there between the Dark Irons and the rest of the Dwarves. I don't know, it could've worked. But they said in the end they thought Alliance could use a more beastial race and Horde a more funny, comical race. Maybe it was on the Cataclysm CE DVD, I'll check that later.