So I've been thinking about the popular theory around starter themes; with fire corresponding to the Chinese Zodiac, Grass corresponding to prehistoric or extinct animals, and Water corresponding to warrior/soldier archetypes.
Now, there are some starters that don't quite fit, particularly with Water with Primarina and Feraligatr. But it's cool they seem to have a loose theme for each of the types.
Looking at it now, the way Quaxly holds its wing reminds me of the cape of a matador. Maybe when it evolves, the wing will look more like the muleta. Like some people have said, the hair of the Duckling looks like a matador's cap, but it could also evolve to look like a sailor's hat or conquistador's helmet. Whether it becomes a bullfighter, Navy sailor, or conquistador, that fulfills the warrior/soldier archetype.
It would be pretty cool if Sprigatito evolved into a lynx for its second stage, and a sabretooth tiger for the final stage. That way, it would turn from a house cat (area of least concern) to Iberian lynx (endangered) to sabretooth tiger (prehistoric/extinct). That would fulfill the prehistoric/extinct animal archetype.
Fuecoco probably has the most potential for going in a different--unexpected--direction, and not fitting the Chinese Zodiac archetype. So far, the only animal signs that have not been used are Ox, Snake, and Sheep/Goat. They could have used a fire-breathing bull to foil the matador, but it looks like they didn't go in that direction (that's not to say we won't see a fire-breathing bull in this region). So the only logical option seems to be that it loses its limbs, and becomes a Snake. However, they already did that with the Serperior line, and we've already had a crocodile starter with Feraligatr. So, while the Fire starter has the most potential for trying something new and creative, it also has the highest probability for a retread.