When it comes to the Square character, despite my appreciation for Mario RPG and Geno as a character, if I'm trying to make this this "Ultimate" fighting game for gaming characters, I'd no doubt at least attempt to get Sora in the game if I was Nintendo and/or Sakurai.
Something of note is that the only "Square Enix" thing seen as a Spirit is Geno. To my knowledge there isn't anything for Final Fantasy, DQ, TWEWY, Crono Trigger, or anything really. Spirits don't mean anything imo but I just thought I'd point that out.
To me, the only way Sora doesn't work out is if Sakurai/Nintendo are intimidated by the prospect of working with Disney (plausible, no doubt), or he costs too much (also plausible).
For whatever reason, playing KH: Dream Drop Distance and seeing the gang from TWEWY made me reconsider Neku's prospects of being in Smash. It was just unexpected. I've never played TWEWY, but I just wasn't expecting that.
I must say though, it'd be terribly interesting if the Geno costume isn't a Mii Fighter outfit and Geno isn't playable. That'd be a huge "O O F" text from me my dudes. Similar to Rex, if we truly aren't going to get them as playable in Smash, a Mii Fighter costume will never replace them, but it's something.