For me in no particular order:
Gunther Arcanus - A Forsaken/Lich Necromancer. In Classic, we were given a questline to recruit him into the Forsaken. However in Cataclysm and to this day post Battle for Lordaeron, he just chilling on his little island and is involved in no quests whatsoever.
Fenris Wolfbrother - The last we heard of him was in the Beyond the Dark Portal novel where he gave the Scepter of Sargeras to Teron Gorefiend and he had returned to Outland. After that, we never hear what happened to him.
Hatock, Groton, and Skal - These are Fenris Wolfbrotherâs three sons. We meet them in WoD. However, we donât know whether or not they even existed in the prime universe.
Thalen Songreaver - The last time we heard of him was in War Crimes where he helped Garrosh escape from jail.
Jevan Grimtotem/Stormsong - He has never made any appearance in the game nor has he been involved in the story after being introduced in The Shattering.
Volâjinâs Children - Volâjin has 3 children according to the lore, one of whom we met in the game named Yenniku.
Magatha Grimtotem - So Iâm curious as to what Blizzard has planned on doing with this character. Is she going to be given a redemption arc or something or will she at long last go the way of the loot pinata?
Meâdan - Yep I know, this one is controversial. Blizzard once stated that they wanted to add him into the game but the employee who stated that left Blizzard in 2016. Iâm curious as to what his whereabouts in the story are right now or if he is even cannon at this point.
Tammis and Clannia Foxton - The last time we ever saw them was in the Lord of the Clans novel. Thrall had ordered Grom Hellscream to give their daughterâs necklace to them after the siege of Durnholde. However the necklace somehow had ended up coming into the possession of the Syndicate and we never hear about what happened to the Foxtons after the fact.
Sergeant - Another character from the Lord of the Clans novel. He was the man who taught Thrall the concept of mercy and honorable combat. He was also one of the few people nice to Thrall during his capitvity. When Thrall stormed Durnholde to break the internment camp system, he allowed Sergeant and his men to go free. We never got any further story for him after Lord of the Clans.
Calia Menethilâs husband and child - In the Before the Storm Novel, we find out that Calia Menethil eloped with a footman from Lordaeron and they had a child together. After the third war, they had lived in Southshore up until Cataclysm when the Forsaken had blighted the town at which point they were separated. We never find out what happened to them after that.
Isiden Perenolde - The nephew of Aiden Perenolde. Last we heard of him, he went to Gilneas to protest who the leader of Alterac should be in the novels. Since then, he has made no further appearances.
What long forgotten characters do you want an update on or to want to see return to the story?
EDIT: Added more characters to the OP that were brought up in this thread