I personally think it's time that Sora conflicts with himself. He's the only character that doesn't really reflect on himself in the Kingdom Hearts series because he's always worried about others. In KH III, I think he should be rebelling, since he'll be 16, if not, older. For once, Sora should willingly give into the darkness. I'm not saying he should become a villain or anything, I just think he should explore his potential as a keyblade master.
Riku has always been the one to think less with his heart, and more with his brain. I think Sora should start out in Kingdom Hearts III differently (a bit more mature) but also as his typical happy, goofy self, and then in the middle of the game he should rebel. I want to see him become cocky and arrogant with the keyblade, thinking he's wielded and mastered it long enough to take on matters alone. He should rant about how Donald and Goofy are slowing him down, temporarily causing a rift between them, continuing their journey on his own. But to make things interesting, to lose Donald and Goofy as party members for the moment, Kairi and Riku should follow him to try to fix things, making them your party members. And this time, Riku can be the one trying to help Sora, instead of the other way around. And this would be Kairi's chance to get closer to Sora, and join them along side their journey like she always wanted to. So through a good part of the game, Sora will be darker and more gloomy until he figures out he can handle all of the pressure that comes with having to save everybody, and what his existence has done to others existence (Roxas, Xion, Namine, Terra, Ven, Aqua, Axel, ect.)
By the end of the game, Sora could be so consumed by darkeness, that this gives a chance for Roxas/Ven's return. With them existing, Sora loses his strength, but in replacement of that, he gets strength from the darkness that consumes him. Then you'll have to fight as Roxas/Ven, Riku, Kairi, Donald, Mickey and Goofy, against Sora to bring him back to the light, depending on whoever you choose as your party members but Roxas/Ven would be first player. And when Sora does become himself again, they all fight whoever the final boss is, ending the "Xehanort Saga" in pure epicness.
Riku has always been the one to think less with his heart, and more with his brain. I think Sora should start out in Kingdom Hearts III differently (a bit more mature) but also as his typical happy, goofy self, and then in the middle of the game he should rebel. I want to see him become cocky and arrogant with the keyblade, thinking he's wielded and mastered it long enough to take on matters alone. He should rant about how Donald and Goofy are slowing him down, temporarily causing a rift between them, continuing their journey on his own. But to make things interesting, to lose Donald and Goofy as party members for the moment, Kairi and Riku should follow him to try to fix things, making them your party members. And this time, Riku can be the one trying to help Sora, instead of the other way around. And this would be Kairi's chance to get closer to Sora, and join them along side their journey like she always wanted to. So through a good part of the game, Sora will be darker and more gloomy until he figures out he can handle all of the pressure that comes with having to save everybody, and what his existence has done to others existence (Roxas, Xion, Namine, Terra, Ven, Aqua, Axel, ect.)
By the end of the game, Sora could be so consumed by darkeness, that this gives a chance for Roxas/Ven's return. With them existing, Sora loses his strength, but in replacement of that, he gets strength from the darkness that consumes him. Then you'll have to fight as Roxas/Ven, Riku, Kairi, Donald, Mickey and Goofy, against Sora to bring him back to the light, depending on whoever you choose as your party members but Roxas/Ven would be first player. And when Sora does become himself again, they all fight whoever the final boss is, ending the "Xehanort Saga" in pure epicness.