Now, I've seen some express disappointment with the possibility of this being true but, there can be some interesting potential scenarios with these characters. Rather than let's say, just Kyo, or just Terry being the potential candidates added to the roster, Sakurai could bring in the source material of the KoF series in full force and design the following:
Team Japan [Kyo, Benimaru, Goro]: We could get a trio within a single slot; similar to the case of Pokémon Trainer (that has Squirtle, Ivysaur, and Charizard), in which players can rotate between the three members of Team Japan. Each character of course has different moves and playstyles, and to switch (or tag out) one would use the Down B. OR, to really add to the feel for the original KoF games, depending on the Stocks for the match, each time your KoF character gets KO'd, another of Team Japan's members comes up. Although in this sense, perhaps the tagging out mechanic would be best left to a Down B command? Dunno.
Now, in regards to each character's traits; Kyo would be balanced, with attacks (Smash attacks, and some Special moves) capable of inflicting burn on enemies. Benimaru would be slightly lighter in weight, however he could be the rushdown type out of the three with some of his moves inflicting shock/stun. Goro would be the tank; capable of taking the most hits. His movement would be rather slow, tho his smash attacks would have the highest launching potential. Grappler type fighting style.
Team Fatal Fury [Terry, Andy, Joe]: Again, a trio similar to Team Japan, yet with their own unique fighting styles. I think in this case Terry would be the heavy damage dealer, while Joe would be the rushdown type. Andy would be balanced.
Team Shiranui [Mai, Yuri, King]: Similar to the aforementioned teams.