I love when people give smarmy attitudes about something that a quick google search proves they're wrong about.
http://www.youtube.com/watch?v=TPF5kGZ7mQM&t=17m14s
I know I saw it on the blue tracker somewhere a while back as well, but I can't find it anymore and it may have just been reiterating what Dave Kosak said there. We only see six Sha in game. The seven heads of Y'shraaj creating seven Sha was from an earlier draft of the story. We only see six Sha in game and they're manifestations of Shaohoa's burdens. The Achievement and in game book may be named "Seven Burdens of Shaohao", but the "burdens" are his negative emotions of which only six(Anger, Despair, Doubt, Fear, Hatred, Violence) are ever defined. It's always possible that they'll release a new Sha in the future and Dave Kosak was just lying to protect the LORE SPOILERS in that interview, but there only being six Sha representing Shaohao's burdens comes straight from the lead quest designer.