@MagnaRoader considering that Joker is more dagger and pistol with the ability to summon a massive battle spirit's manifestation to hover behind him guardian demon style, I'd say he rather stretch the definition of sword fighter a bit.
This said I was thinking about it but with his inclusion I feel the introduction of a dragon quest hero character is that much more likely.
In Japanese RPGs, Final Fantasy, Dragon Quest and Shin Megami Tensei/Persona are the "big three" of the JRPG tradition.
With FF7's Cloud already present in the game, Persona 5's Joker soon and potentially Dragon Quest's Erdrick/Luminary it might mean Nintendo could be about to have all three represented in Smash.
And with ports/localization of Dragon Quest XI and Dragon Quest Builders 2 soon releasing on Switch and rumors of Persona 5 potentially getting ported too, all three franchises might be directly represented on the Switch itself to cement it as "the" jRPG console.
Like even the more recent 3rd party additions of the Belmont are characters with a franchise that are close to the boundaries of the rpg genre(even if not the direct games of the characters themselves) I can't help but feel it might not be a coincidence.
And from a technical standpoint it makes sense; RPGs are renowned for the variety of skills, spells and gear used by their characters which makes that much more material to draw from when developing move sets. I can only imagine the trickery that might be possible if a Dragon Quest hero comes with the hero class-exclusive kaklang spells that turn the character into an immovable immobile invisible chunk of steel for a short time. Imagine being next to the edge of a stage, weakened, and an enemy come charging at you with a dash attack and suddenly... kaklang, you're a lump of steel and in their surprise they accidently slip past you and off the stage forcing them to recover just as you become mobile again and ready to strike back while they stand unbalanced.
And that's not mentioning the many buffs spells that are a tradition of the DQ playstyle, many available to the hero class.
Even as a sword fighter the character might end up more an hybrid of Link sword&shield with a dash of pikachu lightning(lightning spells are iconic and exclusive to the hero characters in the dragon quest franchise) and perhaps some self-buff spells.
I could picture it. Sword and shield standard attacks.
Neutral B fireball spell(frizz)
Side-B lighting strikes or ground based advancing fire columns(zapple or sizzle lighting and fire group targeting spells respectively)
Down-B self-buff spell. Either the fore-mentioned kaklang or simpler defense buffing kabuff spell.
Up-B teleportation "Zoom"(fast travel spell of the franchise) spell, likely working akin to Zelda's teleportation spell but without the ability to deal damage(and perhaps a funny nod to the "but hero bumped his head against the ceiling" message we'd get in the original games when trying to use it indoors).