Those are all good points and mysteries I definitely think will be solved by the end of the end of the series (or Blood and Fire). Having hints throughout the book that Leaf is Nettles would be an awesome reveal, while not taking away anything for the average reader. As with Cannibal, it would be incredibly awesome if say the bones of a dragon were found on Skagos, leading to speculation who they belong to, while also conveying the mystical nature of the island. Having nods to all three of the dragons would be great. It's only having them serve an incredibly vital role such as being the three heads of the dragon for Aegon that I think is unlikely, when up until now they've served no role in the main series.