>>50149472At this point, Dragon is no longer the overpowered late game type in Game Freak’s eyes. Dragon has become increasingly common in the mid game, with certain Dragons that are deliberately made weak on purpose available very early on. We have had Turtonator available in SM’s equivalent of having five badges. Partner Pokémon fully evolve around that point anyway, so there is no real harm in giving Fuecoco’s final stage the Dragon type. Plus, we have yet to have a fully fledged Dragon partner Pokémon, with Mega Charizard X and Mega Sceptile only gaining it temporarily. And Fire is such a terrible defensive type anyway that Dragon barely insulates it. Meanwhile, Fire/Dragon have good offensive potential but are held back immensely by Dragon not hitting much super effectively, and Water being omnipresent. We do not know exactly what this Pokémon is based on thematically, but reptiles have a loose connection with Dragon anyway. All the same, this does mean that other types can also be appropriate.
Personally I expect Ground or Steel over Dragon, but Dragon is not that unlikely.