The Sha of Chaos!!!
I've been doing a bit of reading into Pandaria lore, and the 6 negative emotions are all over the place in lore. They're in The Seven Burdens of Shaohao.
http://www.wowpedia.org/The_Seven_Burdens_of_Shaohao
Also in The Dark Heart of the Mogu we see mentions of the 6 negative emotions. However, look at this sentance. " And the resulting disarray in the capitol left the empire in chaos for over two years while the saurok melted back into the wilds and disappeared..." It seems after all 6 emotions are felt or conquored Chaos emerges. This is also true in The Seven Burdens of Shaohao, where The First Emperor conquers all 6 Sha and the sundering happens. Given it doesn't happen as a direct result of the Emperor, but the Emperor knew it would happen as in a vision, and set out to conquer the 6 sha to try to save Pandaria.
What's this mean for us? Alliance and Horde are in a war, all of the 6 negative emotions have been slain, and yet Garrosh seeks to control the power of the Sha for himself. Remember the divine bell quest in 5.1? Here's what is said for Alliance side after you kill Ishi and destroy the Divine Bell.
"
Ishi says: Warchief! I... I have failed you.
Garrosh walks away from the bell and stands in the center of the platform.
Garrosh Hellscream says: Yes, Ishi. You have.
Garrosh turns to face Anduin.
Garrosh Hellscream says: Your interference has cost me a great warrior, young prince. You'll pay with your life.
Anduin Wrynn says: That is where you are wrong, Garrosh.
Anduin Wrynn says: The mogu made the Divine Bell to create chaos, but the pandaren created a special mallet to turn the echoes of that chaos into perfect harmony. That mallet was hidden for thousands of years, until now.
Anduin leaps upward and performs an overhand strike on the Divine Bell, stunning Garrosh and causing the bell to crack violently.
Garrosh Hellscream says: Die, whelp!!
Garrosh pulls himself together, closes the gap, and strikes at Anduin, but hits the Divine Bell, shattering it. The bell crumples in a heap onto Anduin, who has been crushed within an inch of his life!
Garrosh Hellscream says: Your Alliance must be at its end if you're sending your children against me.
Garrosh turns to face the adventurer.
Garrosh Hellscream says: I will let you live so that you can tell your King of the price for his continued defiance!
Garrosh mounts his wyvern and takes off, laughing "
Through all these subtle hints, I"m almost certain that The Sha of Chaos will be the 7th Sha, and the one we will ultimately be fighting with in Garrosh who is consumed by chaos, with in his own faction, with in this blind war, with him him conquering all of Kalimdor.