There has been little information revealed about Pokémon Sword & Shield so far, but there is at least one part of the game that is going to be determined by the fans, as CoroCoro magazine is running a contest that will allow the readers to name an upcoming Steel-type move in the game.
According to Serebii, the upcoming May issue of CoroCoro will include a contest for fans to name a move that will appear in Pokémon Sword & Shield. The attack will be a Steel-type move, with a base attack score of 140, but has the side effect of reducing the user's hit points by 50%, which sounds like a major drawback for a move that isn't as powerful compared to some of the attacks used by other Pokémon in the series.
The introduction of a powerful new Steel-type move seems to tie into a rumor reported by PokéJungle of Pokémon Sword & Shield only including a single Legendary Pokémon that resembles a wolf, but its form is different depending on the game. It's believed that this is the reason why Pokémon Sword & Shield logos feature a wolf-like creature on them.
The type of the Legendary Pokémon will be different depending on the game, with Pokémon Sword transforming it into a Dragon/Steel-type Pokémon, while Pokémon Sheild will transform it into an Ice/Steel-type Pokémon. It's possible that this unnamed move will be used by the new Legendary Pokémon, as it always has a Steel-type as part of its typing.
The upcoming Steel-type move in Pokémon Sword & Shield will not be the first attack in the series that was named by the fans, as Draco Meteor was also the result of a contest. CoroCoro once ran a contest before the release of Pokémon Diamond & Pearl for the fans in Japan to name a Dragon-type move, and Draco Meteor (also known as Meteor Shower in Japanese) was the winner.
The new Steel-type move seems like it won't be very useful, as there are other moves that deal as much damage that have lesser drawbacks, such as Focus Punch, Giga Impact, and Eruption. It's possible that the move will be tied to a gimmick used by a specific Pokémon, such as switching to a more defensive form when losing health (in a similar manner to Aegislash's transformation), but that remains to be seen.
Pokémon Sword & Shield will be released in late 2019.