I'm surprisingly fine with no new subclass. Both times they've done that they've integrated the subclass into the story which ends up being shallow and a distraction from the actual story. The best expansion they've released, witch queen in my opinion, didn't have a new subclass and that allowed them to focus on the story. Everyone loved the story and the atmosphere and I'm glad with this expansion they're focusing on the story and not trying to shoehorn a new subclass into the last expansion.
Plus it makes sense that we'd get new light supers when we are literally inside the traveler, the being that gave us the light. It makes sense and another darkness subclass would clash with that story beat, I think.
I just hope the episodes are good.