I think there’s plenty of precedent for a Final Fantasy character to come with a dearth of Final Fantasy character licenses. Sephiroth coming with one Mii Costume and it being the reused Chocobo hat doesn’t seem crazy far-fetched to me. Cloud only coming with a Chocobo costume to represent his series with was weird even back in Smash 4. Plus, although the 3rd-party Mii purge makes the Chocobo costume not coming back irrelevant, the only Final Fantasy Spirits in Ultimate as of now are Cloud’s fighter Spirits... and both of them only used his fighter render despite high-quality full body promotional Cloud renders existing. Yes we’ve gotten other Square Spirits since, but when you think about it, Square has consistently been EXCESSIVELY stingy with licensing out the FF7 characters for Smash, even just as PNGs, and that’s a fact entirely unrelated to any music licensing issues Square characters come with. It’s possible Sephiroth’s spirit board will be filled up with Final Fantasy enemies instead of characters, or maybe the FF7 cast will only come in as Spirits but not as costumes, depending on how picky Square chooses to be. The only weird thing is the lack of presence of other Square Enix costumes considering Dragon Quest got a few, especially with the 2B costume rumors, but the concept of Barret & Tifa & Aerith & crew not getting costumes actually makes sense to me based off of what we’ve seen.
Oh, as for a Mii showcase, they could just... not have one. A minor Chocobo hat highlight and that’s it.