The 7.3 PTR development notes have been detailed on the World of Warcraft forums by community manager Lore.
Following the events on the Broken Shore and the Tomb of Sargeras raid, players are being tasked to take the fight to Argus, the home world of Legion. Lore stated:
“We’re really excited about this update, and are looking forward to hearing your thoughts and feedback as we head into public testing. There are three main areas to explore on the planet, the first of which is available for testing on the PTR today!”
Within this first build, the first couple of chapters of the 7.3 storyline will be available, with enhanced casting animations for both Elemental and Restoration Shaman, Restoration Druids, all Mage specializations, as well as Discipline and Holy Priests. Player feedback is also encouraged with this patch as with all other patches, to help the team work on updating animations further.
This build will also feature new world quests, professions updates with epic gems, and a new dungeon known as the Seat of the Triumvirate. Players can also take part in the new Antorus, the Burning Throne Raid, though as with other Legion raids, it won’t be immediately available with 7.3. The Netherlight Crucible will also allow players to upgrade Artifacts in a new method of customizing relics.
Several other fixes and improvements have been made to existing features, so be sure to contribute your feedback to help aid future fixes and enhancements. You can find the full set of notes over on the official forums.