maybe Garrosh is possessed by the Sha of Destruction. He'll be the last normal mode raid boss... with the Heroic extra (like Algalon, or Sinestra) encounter being Y'shaarj?oh wait... Sha of Despair was a quest mob in Krasarong Wilds.There is also a Sha of Hatred in Shado-Pan Monestary.
Or maybe he'll be after the 7th sha and be possessed by Y'shaarj.
that could also work out well, lore-wise.
I figure his anger and blood lust will be enough that he'll be the reason Y'shaarj comes back.