So it appears Nathanos will be a raid boss

[Spudnik-stormrage]

Shadowlands Alpha build 34081 didn’t add many new NPCs, but [Nathanos Blightcaller] (npc ID 169035) was one of them, along with [Calia Menethil], a character poised to take over Sylvanas’ role leading the Forsaken after the events of Battle for Azeroth.

Nathanos in Battle for Azeroth seemed nearly as unstoppable as Sylvanas, showing up in all major storylines and escaping unscathed, even from Tyrande after she transformed into the Night Warrior.

You can read the salty Nelf tears through the post.