With the Disney worlds announced for KHIII so far, I have some theories about how Sora will get further character development.
Olympus Coliseum: The fact that he rarely tries to understand things for himself. Sora would call himself a big idiot for not understanding that he's the one who reopened the Underdome. If he finds out that is.
Kingdom of Corona: We all remember what Rapunzel's personality was like in Tangled. So she will remind Sora of how naive he's been.
San Fransokyo: Vengeance is one of the major themes of Big Hero 6. And the game is telling a post-movie story of it. If Sora learns about Hiro's backstory, loss, and what he went through, he'll probably become a teeny tiny bit more assertive. Sora's tendency to act like he's never been wronged proves why. Like Kairi being kidnapped by a certain red haired Nobody.
With the Disney worlds announced for KHIII so far, I have some theories about how Sora will get further character development.