Good day everyone. I'd like to share this here
article from last year in which Sakurai talks about his days playing at the arcade, and the lesson he learned then of being mindful of all types of players. A little something to note is him mentioning that back then he was playing King of Fighters 95. What's to note from this title is that, aside from the obvious of it being the direct sequel to KoF 94 (which has the intro scene that would be FITTING for a Smash reveal), KoF 95 also has the inclusion of a sealed invitation within the
intro .
In addition to the former article, there's another in which Sakurai touches upon character choices. This
article is from back in 2015, and one of the things Sakurai seeks in a potential character for the roster is uniqueness. Taking into account that Sakurai is knowledgeable of the KoF series, thus knowing the mechanics of the source material (the team fights), and him having worked on Pokémon Trainer's design (three-in-one character), I could see it possible for him incorporating the SNK/KoF rep as a trio of characters which would include Kyo, Benimaru, and Goro, which formed Team Japan back in the early KoFs. True that in the games you could not tag out and switch to other team members, but the mechanic could be worked around somehow. However, I wouldn't rule out the possibility that instead of going full-on source material, the character trio would consists of the most popular KoF characters, and not a specific Team from the series (i.e. Kyo, Terry, Mai; or Kyo, Terry, Nakoruru; etc.).
Also, let us remember that in EVO 2019, SNK teased King of Fighters XV (currently in development) so, that could go along with plans of promoting the series with the inclusion of KoF characters in Smash prior to KoF XVs release.