This thread is starting to slow down right now, so I'm gonna propose a new question: Of the 3rd-parties that already have a character in the roster, assuming any of them would get another character, what would each of their candidates be?
My theories:
Konami: Theoretical next fighter would likely be Bill Rizer, with Lance Bean as an alternate costume.
SEGA: Either Arle Nadja or a second Sonic character (most likely Dr. Eggman).
Capcom: Possible candidates are Chun-Li, Dante, Phoenix Wright, Morrigan Aensland
Namco-Bandai: Probably either Yuri Lowell, Velvet Crowe, Nightmare, Yoshimitsu, Agumon, Solaire, or the Chosen Undead.
Square Enix: Possible candidates include YoRHa 2B, Sora, Neku Sakuraba, and Lara Croft
Microsoft: The most likely would most definitely be Master Chief, and other candidates include Fulgore and the Battletoads.
SNK: Since Terry Bogard and the rest of his Pass's content pretty much reps the entire SNK company pretty well, the only thing that seems lacking would be more Metal Slug content, which in my opinion, makes Marco Rossi the most likely 2nd SNK rep.