here's my atempt to predict MoP's first tier sets
Warlock: Warlocks always get to dress up as the villains. necromancers, twilight cultists, old gods, et cetera (even if the villains have nothing to do with warlocks :P). so the easiest guess here is a Sha set. Confirmed;
Warrior: As warrior's usually get armor based on the toughest guys around, I'd say their set will probably be based on the Mogu or on the Black Ox pandaren clan. The warrior t14 is out, but I have no idea what it's supposed to look like. Since it has horns, it MIGHT be based on the black ox clan;
Rogue: Rogues have been getting their set design from the dark-ish mobs that always attacks in big numbers, so I'd guess they will get their set from the Mantid or from the Shado-pan pandaren clan (aka pandaren ninjas);
Shaman: For some reason I have a feeling the shaman set will be based on the Red Crane pandaren clan, as they are very close to the element of fire or maybe on the Jinyu, who are known to stick their staffs in rivers and hear what the land is saying;
Hunter: Hunters are known to get sets from what they will be hunting (from warp stalkers to gronn, from murlocs to dragons), so it's hard to define what aspect they will take on (no pun intended ). I would bet on the Hozu or on the White Tiger pandaren clan;
Death Knights: Skulls, bones, the usual :P;
Druids: Druid sets are usually based on plants. While we haven't seen much of the pandaren flora, I'd say the safest bets would be the cherry trees we see in the shado-pan monastery (prepare yourself to wear pink ) or a bonsai tree;
Priest: Cloud Serpent;
Paladin: Tiger;
Mage: No idea