I’d love to see the return of classic villains like the Scarlet Crusade. They’d make much more sense than the speculated “Yrel invasion from an alternate timeline” imo. Especially if we are successful in preventing Nozdormu’s corruption.
I will be excited to see what role the Ethereals would have. I wonder what a “holy” Ethereal would look like. Given their story of how their world was destroyed it would make sense for some of them to turn to the light.
I think the theory that Iridikron is using The Light was because he was essentially a “mirror” of Neltharion in a way and just because of how he looks.
Though narratively I think it would be interesting if he was meant to be a mirror of Deathwing, but with the light instead of void.