Originally Posted by
Soulwind
I don't think that's possible. So far we've defeated: Onyxia, Nefarian (twice), Ragnaros (twice), C'thun, Hakkar, Kel'thuzad (twice), Gruul, Magtheridon, Lady Vashj, Kael'thas, Illidan, partially-summoned-Kil'Jaeden, Malygos, Sartharion, Yogg-Saron, Algalon, Anub'arak, The Lich King (or at least Arthas), Empowered Cho'gall, Sinestra, Deathwing, six different Sha, Empress Shek'zeer, Lei Shen and Ra-Den.
Garrosh is way too weak for a final raid, let alone expansion, boss. He is evil by himself, but he will need more power to make the fight interesting.
Unless the final boss is him using the artifact to throw different monsters at us and, once we destroy them all and the Heart itself, he desperately attacks us and is easily killed off, à la Arthas piñata.