Imagine if Fuecoco gets the Fire/Dragon secondary type lol. Charizard fans would be furious.
It won't happen, because the Dragon type is too powerful for starters. It's already resistant to Grass, Fire, Water and Electric, and Fire/Dragon cancels Water's, Ice's AND Fairy's effectiveness. You could give them Dragon moves, but their usefulness is going to be very limited. People will be quick to point to Empoleon's Steel typing and its many resistances, but in Gen 4, Torterra and Infernape also had typings effective to Steel (Ground and Fighting, respectively), so everything was this balanced.
For my part, a Grass/Dark smilodon, a Fire/Ground linnorm (literally a a serpertine dragon from Norse Mythology) and a Water/Fighting waterfowl* sailor would be my pick ^_^
*"Waterfowl", of course, defines any marine bird. We had a seagul evolving into a pelican, but those species aren't from the same family (
Laridae vs
Pelecanidae). A duck comes from the
Anseriformes order, which include ducks, swans and geese, but it could evolve into another marine bord, like an albatross from the
Procellariiforme order. We currently don't have an albatross or a goose in Pokémon... and if the later is introduced, the Untitled Goose Game memes are going to
flood the Internet (pun intended XD ).
Grass/Dark is a typing we haven't seen in standard play since Gen 3 with Shiftry and Cacturne, while Zarude is often forbidden.
Fire/Ground is a typing we haven't seen in standard play since Gen 3 again with Camerupt.
Water/Fighting is a typing we haven't seen in standard play
since Gen 1 with Poliwrath, while Keldeo is mythical and Urshifu is legendary.