Here’s my thoughts on speculation going forward:
The biggest winners of Kazuya are to me, series or companies that already had Mii Costumes in the DLC. To me, the biggest benefactors are the following series and companies:
-Ubisoft had that whole Byleth situation. It’s possible that they settled for Mii Costumes in FP1, but are coming back with a character in FP2 now that we know that Heihachi wasn’t ”saved“ to return later. It’s a decent enough plausible deniability to give Ezio or Ray-Man a fighting chance, especially with the base game Ray-Man Spirits possibly fitting a second chance theory as well.
-Capcom I think is back on the table, although it probably won’t be Monster Hunter. It‘s very possible the costumes were a “strike while the iron’s hot” type of deal, and that the Capcom character is still coming up.
-Zelda is back in a position to not be hampered by the FP2 bonus costume.
-Splatoon doesn’t have to worry about Callie & Marie either.
Some other thing to take into consideration is the status of Spirit Events. Their deconfirmatory status was based on the similar premise of “saving” the Spirits for the Spirit Board, I don’t think Spirit Events are a particularly “hard“ deconfirm anymore.
Some Spirit events to keep in mind:
-Pokémon. The Pokémon Spirit Event was released for the launch of SwSh iirc. Since then, it’s gotten DLC and probably five new series of anime.
-Paper Mario: The Spirit Event that didn’t even include Paper Mario himself. Plus, Paper Mario is much more than Origami King and Paper Mario and in terms of content, we’re missing a good amount of partners for example.
-Astral Chain, Ring Fit and Resident Evil could happen but eh, you know.
I still think the biggest winners however, are characters that recently had a game come out. Corrin was very much picked at the end of his DLC run for this purpose, and I’d scratch my head if they planned a fighter’s pass that ended two years from the time where they decided on the characters, without using a slot for something on the horizon like at least the Smash 4 DLC deliberately aimed to, and what was possibly the driving force behind Byleth as well.