Having him show up and be part of the planning (if we intend to show any of the planning for the Dagor Bragollach) might be in play; you don't expect a dragon to be a strategist.Last season, there was talk about spreading out the reveal of Glaurung's powers; consequently, we did not show his ability to speak during his attack in Episode 13. We did show that he was capable breathing fire and hypnotizing some Elves with his eyes.
If we want to save the reveal of Glaurung's ability to speak for the Dagor Bragollach, we will have to show him not speaking in any scenes of Angband before that. That might make it difficult to portray him as having any part in the internal politics of Angband. Or, we could simply forget about what we said last season and show Glaurung talking to the other villains this season.
Another possibility would be to differentiate between Glaurung's ability to speak and his ability to speak with the kind of persuasive, hypnotic power he later uses on Turin. Perhaps we could have Glaurung speak normally in his conversations with other villains in Angband, use some kind of musical cue or transformation of the actor's voice to indicate when Glaurung is casting a spell with his words, and then reveal this ability during the Dagor Bragollach.
I could envision a potential scene where Glaurung is attacking Maglor's Gap, and Maglor orders his soldiers not to look into Glaurung's eyes because that's how the Elves know he is able to hypnotize people. The soldiers obey, but then Glaurung starts talking. Maybe he counters Maglor's orders or calls out to Maglor personally, but either way, the morale of Maglor's soldiers fails, and Glaurung wins the battle.