Redshirtguy kind of gave a list of what we’ve seen so far from the PTR:
-New Questline for blood elves only.
-New Hawkstrider mount and Blood Knight transmog set, presumably form said blood elf questline.
-Items implying a similar new questline for Dark Iron dwarves.
-New darkhound mount and set of Dark Iron dwarf themed transmog weapons, presumably for said Dark Iron questline.
-New map of Tirisfal Galdes with a reconstructed Brill. The map is attached to an encrypted questline and a new (also encrypted model for Calia Menethi.
-New silvery color for the cheetah travel form from 9.2.
-New area in Stormwind that’s just a random stable outside the stockades using kul tiras assets
-Orgrimmar guild vendor area removed and relocated to a different location in the Valley of Strenght
-New Stay Awhile and listen conversations between Taelia and Bovar, Jaina and Khadgar (Alliance Only), in Oribos.
-New HD skybox for Hillsbrad Foothills.