When getting over-excited about the
But maybe that's not the important bit. Pandaria may be the setting, but perhaps the theme of the expansion is actually being driven by the first word of the title: mists. There's an unfinished story from Cataclysm that has always felt as if it needed a sequel: that of the Kvaldir. We don't know much about them, other than that they attack the land from the mists, can summon kraken, and they are at war with the Naga beneath the sea.
That would tie the expansion neatly into the previous two and starts to shape the factions we might see, Proabably Naga and Vrykul as the main threats, with the Pandaren as the local friendly NPCs. Sadly, I think it's hard to see Blizzard assigning Pandaren to player characters to either of the current factions, as it would cause to much annoyance to the side that didn't get them. Lore-wise, they'd probably be slightly horde-inclined (as were the goblins), but it would be easy to update the story in the light of recent events to amend that. All it would take would be (for example) a Pandaren leader being rescued by an Alliance ship to shift that slight connection.