Get your hopes up? Sorry, I'm a jerk. Although, given that Blizzard has released new spirit beasts on a fairly regular basis with large content patches, it's not out of the question that we'll be seeing another one with the release of Cataclysm. It's all speculation, but given that the looks of the four current spirit beasts consist of two cats (let's be honest, Loque looks a lot like a cat), a wolf and a bear, would it be out of the question for the next one to be a boar? Those are four fuzzy, non-flying mammals. Honestly, gorillas seem out of the question because they would be, without a doubt, the ugliest spirit beasts imaginable, and rhinos are already exotic; all four previous pets in their non-spirit form can be tamed without Beast Mastery.
Ruling out all other current normal pets that aren't fuzzy, four-legged, non-flying mammals, the only other possibility could be the hyena, which I admit would also have the potential to be very cool. So what do you think? What spirit beast would you like to see next? A whole new model introduced in Cataclysm? Personally, I wouldn't mind adding a glowing green boar to my collection.