Future Expansion Pack possibility. (Possible spoilers)

In one of the first trailers made for Diablo 3, a small clip featured a demon that we all assumed was Diablo and it had 7 heads. [For those of us who beat Diablo 3, we know Diablo did not have 7 heads.][/spolier] In Diablo lore, the universe began with the battle of Anu and Tathamet. Tathamet was the embodiment of evil and Anu was the embodiment of good. Tathamet was a seven headed dragon that was the first prime evil, which may have been seen in that trailer as a hint of a possible future expansion pack. (Or of course they may have changed Diablo's looks, but hey you never know.)