So there will be 6 new rare mobs in 5.1. 3 Horde and 3 Alliance.
Loot tables include three, 1 minute cooldown trinkets, only usable on Pandaria.
One being a loss of control trinket.
One being a +10k pvp power trinket. [that's 37.74% increase at 90, oof]
One being a +10k res trinket.
Other drops include an invite to the Brawlers Guild and a token for 250 honor.
Also, it looks like they have new ability sets compared to current rares.