Imagine if the Garrosh we know has been an imposter the WHOLE time. We have seen it before with Shades, Dreadlords, and Dragons. Can you imagine if the Garrosh from Cataclysm was somehow captured and replaced? I remember a Garrosh that actually had honor. I remember a Garrosh that was so furious that innocent Night Elf women and children were killed by a mana-bomb that he threw a General off of a airship platform. I remember a Garrosh that almost kills you for using demonic powers to defend Splintertree Post and demands the demon's head that attempted to corrupt the Horde with fel magic. I remember the last time we REALLY saw Garrosh Hellscream kicking ass was when Deathwing's drakes attacked his ship and he crashed into the ocean.
Things seemed to change after that. When he returns, we was suddenly way more aggressive, he kicked most races out of the center of Orgrimmar, and he started using tactics that we had just seem him have issues with not long before... wiping out Theramore with a mana-bomb. He then proceeds into the downward spiral we have witness in Mist of Pandaria.
Like all expansions, after the final raid is release and the story is told, there is always a lead into the next chapter. Quests with Wrathion suggest that the next force we fight is going to be from beyond Azeroth, and that the Horde and Alliance will have to work together to stop it. Even in the quest lines, the images that Wrathion displays to the player is that of felfire falling from the sky, which strongly suggest Infernals and the Burning Legion. What if the Garrosh that is so out of control now is just an imposter set in place long ago? Kil'jaden, Varimathras, Balnazzar, Mephistroth, Detheroc, even Magatha Grimtotem... they are all still out there. What if the Garrosh Hellscream that we have come to know and hate so much is just a place holder for the Burning Legion's return, and the real Garrosh Hellscream is just a prisoner.
With all of the internet rumors about Burning Legion, Queen Azshara, and the Dark Below, it seems fitting that the races of Azeroth would be tricked into war and softening ourselves up for another invasion. This has all happened before, when with Burning Legion created the Lich King and the Scourge to kill everyone in preparation for their arrival.
I am in no way rooting for Garrosh, in fact, if I could choose anyone has a Warchief I would pick Varok Saurfang, but something tells me that Garrosh Hellscream, the REAL Garrosh Hellscream, is going to be the Warchief... and he is going to be really pissed off that someone has messing with the Horde.