Summoning other characters would mean creating models for all of them - I could imagine the Nightmare Geese being used in the story as a tease of the alternate FF/South Town games reality (I know at least one of the Super Robot Wars does something like this, having a Getter Robo character become aware of his death in an alternate version of the franchise), but enough different ones for a complete moveset... I like the thought, but after 50 different models and animating all of them, I'm not really sure...
That exactly why the extra sprites that started popping up in the mobile games bonus cards and XIII's achievement pictures really seemed like perfect teases. Sure they might not have had the money or time to make, say, Geese or Heidern into full characters, but a few frames that could pull off a move or 2?
Same idea in 3D; fully making models for characters is one thing, but a few simplier models with some unique motion data, no new VA work, and no over-concentration of lip synching, exaggerated physics, or making unique effects?
Also kinda wouldn't work for a character that is supposed to be a part of the playable roster.
Here's hoping for someone cool and memorable. Maybe the first female final boss?
Eh, wouldn't be too much different than Sonico in
Nitro+ Blasterz. Or even Chizuru sending out mirror images of herself to attack. And lets not even mention Gargos's sending out 2 assist to help him battle in new KI, the minions Blackheart summons in the Marvel games for basic button presses, or Chang in CVS2... there's loads of ways to make a "group" into a single playable character.
And it always seemed like an appropriate end boss for KOF, to actually throw a team at you, rather than a single combatant.
Heck, I'd "settle" for 100 demon night in a 3D graphics fighter:
