They do hint at it. This scene is so much better, and a logical result of the story line — how to deal with Meeren’s weaknesses while Dany has disappeared — than the Jon Snow-Drogon petting zoo:
It’s a fantastic scene that combines exposition (Tyrion displaying his knowledge of dragons and their history, as well as his childhood love of dragons) with danger (risking his life to release the dragons from their chains), proof of dragon intelligence (the first dragon lets Tyrion stroke his neck before removing his collar, while the second one approaches, then bends down and extends his neck so Tyrion can remove his collar) and crazy foreshadowing (is Tyrion really a bastard of the Mad King, and thus the third head of the dragon?).
The wildfire idea is interesting, but I just researched a few fan sites, and nobody thinks it is as hot as dragon fire. But wildfire is explosive, so if it hit a dragon in the face, perhaps the explosion could affect the eyes.
It’s sad that our little party is ignored by the rest of the world. I’m going to the Ringer.com less and less, as most of the articles are either repackaged summaries of clips from the Talk the Thrones after show, or superficial surveys of the staff on future predictions. Ask the Maester is still a very good source of GoT content.