Maybe playing as them was triggered by a reaction command seems more realistic. Like say Sora got trapped in a battle by a particular attack move by...
I'm kind of hoping that they spred the lights through the worlds and each party develops their own part of the story, like what ffxiii did. I dunno I...
I'm no expert, and frankly have no idea how long it takes to even make what we can see from the trailer, but I wouldn't be surprised if they started...