Mythic gets it own adjusted model. PVP elite gets its own adjusted model too. I'm guessing that is what the top two are for.
Heroic will get one of the colors as will normal. That leaves two. If they don't do tier look-a-likes in LFR come Legion, either the PVP armor will (maybe) be a Horde/Alliance thing or two of the colors are getting shelved. Or they'll just use one for PVP.