That is a good question. I feel like there’s a possibility of another Greninja situation where they have Sakurai dome advanced knowledge so he could work on the character. If not, we could potentially see another older character like Elma or Nia. He would likely have no knowledge of the Xenoblade X remake at the time but Elma was always a pretty popular character.
I just checked and Xenoblade 3 was anounced in February 2022 (3 years ago), so technically Sakurai at least knew of Noah (and Mio) for 2 months before the plan, asuming the plan is smash of course, so i think the greninja situation you said it's possible as well, Xenoblade 3 was probably very, very far into development in April 2022, if not nearly done, so i think it would be possible to make a complete moveset of Noah (or Mio) by then.
If the roster was drafted in 2021, I think it's highly unlikely for us to see Noah or Mio, as sad as that is.
There's always DLC though.
EDIT: I don't think we'll see Elma ever unless Xenoblade Chronicles X takes off as a series and she's still relevant in it; The remake itself isn't going to get her in.
Wait, i though it was drafted in April 2022, did i misunderstood something?
I know that possible character trailer ideas is meant for Character discussion threads (When another Smash Bros is announced to begin again), but I'll take a shot for a bit. If Shadow the Hedgehog become the next fighter, how would you think his trailer could play out? I can add that The ARK can be the stage for shadow.
Speaking of Shadow, kind of a shame that's probably too late for having Shadow Generations moves for Shadow.
As for his trailer? Something Black Doom related, i think he could make a cool AT or Boss for the base game, but the chances are very slim as this game might have been drafted pre-Shadow Gens.