Would a Bravely Default character work? I'd say Octopath, but Bravely has a bit more time on its belt. I haven't played much of the games themselves, but I think they revolve around class changes? How would that work in a moveset?
I think a lot of people envision a stance change moveset: kinda like Pokemon Trainer's down b. However, I don't think that's too likely, since that is not only a huge amount of work, especially for a dlc fighter, but it also makes for an inelegant moveset imo. The most I could see come from this moveset concept of class change is being able to swap special moves.
My alternate concept revolves around the game's namesake: the Brave/Default system. In the BD games, you can Default, which sacrifices a turn but doubles your defenses and stores that turn for later, then Brave taking multiple actions in one turn. Or you could Brave right away, but leave yourself vulnerable for as many turns as you braved. And there are some high powered moves that require Braving to preform.
In smash, I think this would manifest as Default assigned to down special, which could power up your other specials for later. but pressing and holding b powers up the special anyway though it leaves you extremely vulnerable. Think Focus Attack plus Limit Break (so, Rebels Guard I guess...) but the buffs are more focused and can be stacked. I realize meters and resource management mechanics have become a trope of Smash dlc, but I think Brave/Default can be made distinct.
Now, if you want to go crazy, you could have it so Braving allow you to cancel normals into specials, but on what would likely otherwise be a highly mobile swordfighter that may be too much.
Thinking on it, Byleth and Hero kinda stole a BD rep's potential thunder. I mean, since the class system in BD is so open, I always pictured Tiz or Edea having a moveset that drew ideas from all over the place, incorporating a variety of weapons and spells. Now, Byleth covers the "weapon's master" archetype well enough, and Hero the "magic swordsman." I guess Sakurai was able to differentiate Hero and Robin enough: they have very different normals, and feel very different to play. Even so, they are quite similar in broad strokes, with a Wind up b, a swaped Fire and Electric attack for neutral and side b, and a utility down b. There's definitely still room to make a BD character work, but it would take some creative thinking for them not to come off as stale.