The fifth ring of Azerite Traits is definitely coming in Tides of Vengeance. You’ll see it on new gear when Season 2 begins, on the same day the Battle of Dazar’alor Raid opens in January. At that time, the item levels of rewards from dungeons, PvP, emissaries, Warfronts, and everything else that drops Azerite gear will go up, and all of the new Azerite gear from those endgame sources will have a fifth ring of Azerite Traits.
In the next few weeks, we’ll advance the state of the PTR to test Season 2. You’ll then see the new ring on rewards, the new Mythic Keystone affix, and other content that’s coming with Season 2.