So this new theory's been making the rounds called Costume Theory. Essentially Joker brought back the Tails and Knuckles costumes for what seemed to be no reason (previously, all third party Mii Costumes were cut), and I think that's because Atlus and Sega (the one with the SEGA logo) are connected through Sega Sammy. People have speculated that this could mean the return of other Mii Costumes from other companies coming with a representative from each. I bring this up because we might actually be legitimately likely if true, since there's some leftover Sega Mii Costumes from last time. In particular, Akira and Jacky's Mii Costumes are still gone, which may be a big, big boon to our chances if Mii Costume theory proves accurate. (Albeit, most of the characters I want are screwed over by it [see Crash, Frisk, Banjo, and basically every first party], and I don't even believe it too much, if at all. But it's food for thought.)
Aside from that, voice clips have only been re-used in eSports/Champions. Every game rerecords the voice clips, even though it's a massive waste of money to do so outside of because they want to change the dialogue or to update the character's voice. But yeah, even a 30 roster game would be better than that godforsaken 24 character limit again, let alone something like 60 characters (hey, if it's a multiple of 24, it'd be okay, right?). I'm buying Champions on Steam, Switch, and PS4 because I want this series to go somewhere in the west, which will mean that in either future DLC, or the next game (if there's newcomers), we stand a pretty good chance at least, even if we can't approach near-lock/open secret levels (think Inklings or Ken tier) of likelihood. Besides, if we become popular first, then this will just be a milestone instead of a miracle. But honestly, I'd take either.
I feel like I'm going in circles, since there's not much left to talk about when it comes to what Arle in Smash would be like. Her moveset is extremely diverse, and all but guaranteed to stand out thanks to either the Puyo or chaining gimmick, she has plenty of stage potential, music potential, and spirit potential. There's just not much left to discuss that hasn't been already... unfortunate.