New Surprise Dungeon Coming to Season of Discovery in Phase 4

wowhead.com:

During the recent Season of Discovery Phase 4 Preview, Blizzard shared details about the new level 60 endgame Dungeons, including «a new mystery dungeon to discover!»

Blizzard

• Blackrock Depths (2^nd half)
• Blackrock Spire
• Dire Maul (3 wings)
• Scholomance
• Stratholme
• Plus a new mystery dungeon to discover!

While datamining a recent build of the Season of Discovery Phase 4 PTR, we noticed a couple of new Dungeon Encounters and an Area update that was added to the build. While «Grimroot» is not an entity that has ever appeared in any version of WoW, Classic enthusiasts may recognize Diathorus the Seeker.

• NEW 3023
  Grimroot
• NEW 3024
  Diathorus the Seeker
• NEW 3028
  Destructor's Wraith
• NEW 3029
  Zilbagob
• NEW 3030
  Pyranis
• NEW 3031
  Hellscream's Phantom

While this NPC existed in the original version of World of Warcraft, the quests related to him did not show up until The Burning Crusade expansion. As a result, this NPC and the Demon Fall Canyon subzone of Ashenvale remained mostly unused in every iteration of WoW Classic, including Season of Discovery.

• NEW 15540
  Demon Fall Barrow
• NEW Demon Fall Canyon
  Directory: 2784
  Type: Dungeon

However, during Blizzard's recent Season of Discovery Phase 4 Preview video, they specifically mention «one more Dungeon surprise» during the Level 60 Content segment of the video. Could this be the new «Demon Fall Barrow» Area that was datamined?

It seems that Grimroot is likely the name of the new treant boss in this area, and it also appears that there may be an apparition of Grommash Hellscream, who historically died at this site while fighting against the demon, Mannoroth. In addition to these clues from the Phase 4 Preview video, there has also been an update to this area within the Season of Discovery Phase 4 PTR.

On the left is an image of Demon Fall Canyon on Classic, and on the right is a screenshot of the same location on the PTR.

It appears that