You know, I also got to be honest
These new Mii costume waves have kind of been Anemic to be honest with you
The fact that there were only 4 Costumes with Pyra/Mythra today kind of makes me tone down the amount I was expecting. I'm going to guess there really is more that goes into these Mii costumes than what meets the eye
And not even just in developing the Costumes, but perhaps the Negotiation. I think the only Costume where I'm unsure on their negotiation timing is Arthur. Vault Boy was probably negotiated earlier than we might expect because Bethesda talked to Nintendo about Smash sometime around E3 2018 (A big part of the reason Doomguy got some much Speculation), Suda's been asking for Travis for awhile now, and the Rest of the costumes already had some presence in the game, or were negotiated with the characters most likely (and character negotiation can depend on when you feel it happened)
If there were many more costumes in the future, I don't think there would only be 4 in this Mii Costume Pass. They seem to heavily be re-using assets to Make their Mii Costume passes, which include Spacing out the costumes so they don't have to make as Many, and perhaps using assets from the game or other games to make their costumes.
I don't know how that would affect Speculation. It does add to a theory I've been brainstorming about FP2 ever since Pyra/Mythra were revealed, but that's my theorycraft, and probably one I don't think many people would follow.