Let’s start with the Draconic deities. I’d model any specialty priests after the entry for Null in Cult of the Dragon, who is actually a combined aspect of both Chronepsis and Faluzure. Since Null has Specialty Priests, I’d imagine most of the other draconic gods have them, too. They’d also make sense for a Council of Wyrms setting.
Io – Io doesn’t seem to be very active with his children, but he does have an interest in them. Priests would probably be pretty rare, although I imagine they would exist. Perhaps something similar to priests of Annam with the giants.
Aasterinian – I see no reason Aasterinian would not have specialty priests amongst dragons. She’d be popular amongst brass and mercury dragons.
Bahamut – As with Aasterinian, I think Bahamut would definitely have Draconic Specialty Priests. He would probably also have a separate priesthood amongst humans and demihumans, just as Tiamat does.
Chronepsis & Faluzure – In their Null aspect in the Forgotten Realms, they have Draconic Specialty Priests. I would see what necessary modifications would need to be made to split the priesthoods to fit in campaign settings other than the Forgotten Realms.
Tiamat – Tiamat already has a priesthood amongst humans and demihumans, so it seems appropriate to create one for her Draconic followers. Tiamat and Bahamut should sort of have mirrored priesthoods.