Ah hahaha! In the Trevorrow script, they named some ancient Sith as Palpatine's master
Kylo Ren, meanwhile, finds a holocron left behind by Emperor Palpatine, meant for Darth Vader, telling him to seek out Palpatine’s master, named Tor Valum, to finish his Dark Side training. It’s not clear if this is meant to be Darth Plagueis or someone else entirely. Naturally, Kylo wants to follow in his grandfather’s footsteps so he goes out searching for Tor Valum.
Tor Valum is revealed to be a 7000 year old “Lovecraftian” alien.
Not only does this sound like one of the ancient Sith Avellone wanted to portray in the proposed K3, its name is very close to my Exile's name.