Along with the Armored Evolution Rumors that first surfaced after the Pokemon Company trademarked the term 'Armored Mewtwo', there has also been speculation that the newest Mythical Pokemon, Meltan, will also play a key role within Pokemon Sword & Shield. If you didn't already know, Meltan and Melmetal (Meltan's Evolution) were the only New Pokemon that were introduced within Pokemon Let's Go Pikachu & Pokemon Let's Go Eevee. Meltan is special in the fact that it's the only Mythical Pokemon that has the ability to evolve, being the bridge between Pokemon Let's Go Pikachu & Pokemon Let's Go Eevee and Pokemon GO since you needed both games to ultimately capture Meltan and evolve it into Melmetal.
Unfortunately, Meltan didn't play that big of role in Pokemon Let's Go Pikachu & Pokemon Let's Go Eevee. And, because of this, it wouldn't be unheard of for it have some sort of storyline in Pokemon Sword & Shield. Both Meltan and Melmetal just so happen to be Steel Type Pokemon, which would play into the theme of Pokemon Sword & Shield quite well, especially if The Galar Region is as industrial as the creators of the franchise have made it sound. Of course, a storyline would also allow players their only way to obtain Meltan in Pokemon Sword & Shield, or at least something to do with the Meltan they will eventually obtain through some Pokemon Event.