Personal Armor Units, as they're known, are TR's version of mounts. The names of five are known so far -- Angel, Ghoul, Grendel, Shiva, and Spectre. According to Paul Sage, Lead Designer of TR, you'll get access to your PAU at level 40. All we know so far is that Grendel is Grenadier only, Spectre seems to be Spy only, and that you can fight in them. These ain't no horses!
There's some details about other end-game content in TR, though whether that will come in the same update as PAUs is anyone's guess.