All throughout Pokemon Sword and Shield, you'll be taking on a diverse lineup of Gym Leaders, just like you would in every other Pokemon game. With the launch of the Isle of Armor expansion though, it seems the Gym Leaders can come hang out in the new land.
The first evidence of the Gym Leaders taking a little break from their usual surroundings came over on the Pokemon Sword and Shield subreddit. One user reported having seen Gym Leader Nessa pop up in a location called the Courageous Cavern, which isn't too far from where you first start out the new adventure.
After that, subsequent users reported finding various Gym Leaders in their versions of Pokemon Sword and Shield all over the Isle of Armor. One person bumped into Gym Leader Bea down by the beach, for example, whereas another player found Marnie's brother Piers in the forest area of the island.
Note that the Gym Leaders can't actually be fought in their new locations. They can just be spoken to a few times for various responses, which makes sense when you think about the fact that they've probably come to this lush new island as a getaway from their usual surroundings, and don't really want you beating them down into the dirt right about now.
Pokemon Sword and Shield's Isle of Armor expansion is out right now, for everyone who owns the Expansion Pass for either game. Later on this year there'll be a second expansion for both games, called the Crown Tundra, taking us to new frozen horizons.