Your guessing is -yet again- not following the data we already have.
Takuma is going to complete Ryuuko Team.
Either Hwa Jay or possibly Billi Kane is going to complete Southtown Rival Team.
Also, Adelheid is most likely to appear, yes. And, Rose is supposed to have a role in the storyline. If you saw Adel's own ending in KOFXI you should know why.
On a side note, the two female appearing in KOFXIII intro among the brotherood of "Those who Came from a Distant Land" are like grown-up versions of those two brats who appeared in various KOF XI endings, recovering Magaki's body and making fun of Heidern during the final debriefing.
Also, in New Psycho Soldier team ending (again, KOFXI) we can see Ron is still watching over Kensou's awakening of his true 'Dragon Spirit' power. As you know, since the original Psycho Soldier, Athena is the embodiment of the Phoenix Spirits, and Kensou is the embodiment of the Dragon Spirit.
Quire surprisingly, in the final shot of the said eding, we can see Ron is together with Misty, LIN and some other persons (on the right). This is odd: pretty much as DuoLon and Ran, Lin is supposed to be hunting for Ron the Traitor (of Hizoku). Maybe Ron's true agenda was to prevent the disaster that Those who Came from a Distant Land are aiming to? Maybe he apparently 'betrayed' Hizoku in order to follow such a scheme?
At this rate, the last missing team in KOFXIII is quite likely to be an 'Hizoku Team'.
It would be soooo cool to have Ron, Rin and Ran in one team.