As unlikely as it is for Sora to be included in the fourth coming game as he is owned by both Square-Enix and Disney, two companies who are notoriously stingy when it comes to use of their intellectual property he is still a very interesting prospect from a fighting stand point. His swift combat from both of the previous Kingdom Hearts main console games not counting all ridiculous handheld spin-offs released since, would make for a seamless Keyblade focused move set that would of course come with his trademark speed and agility.
He has just as much potential with other attack forms like his magic used in his previous games which could be the basis of his B move set to compliment his ever so heavy smash attacks given by the A button. You could also charge his Drive Gauge if they could find a way to creatively implement it so you could use such awesome KH related moves like Sora's drive forms and summon abilities. These would be especially useful as specialty down B maneuver. If not for B button specialty attacks then save them for something epic like a Final Smash if those actually make a come back
Now it isn't a completely impossible scenario as Sora has appeared a handful of time on Nintendo's hand held consoles as thats where the majority of Kingdom Hearts non-sequel spin-offs have been released for. It's just the companies that actually own him aren't really the type to collaborate for such projects and like to keep their properties to themselves. If he ends up making an actual appearance then color me pleasently surprised as he is among the top of my dream roster but the likely hood is that it's just that, a pipe dream. For more of my opinion on this subject please watch the video below.