While the RPG series is mostly known for its fighting mechanics, Kingdom Hearts 4 will naturally deal with a fair bit of magic since it's imbued in the series' lore as well as its combat. Between the strange nature of the Keyblade and the war of Light and Darkness in each person's heart, magic in Kingdom Hearts is as varied as it gets and works in unpredictable ways. With each entry, the magic systems end up being capable something surprisingly new each time.
That said, there's likely more excitement involving the next numbered KH title than there's been with the others as Kingdom Hearts 4 is purposefully taking on a new direction compared to the others. This time, Sora's in an entirely new world, likely with a new set of rules. While the trailer makes it clear that he's still the Keyblade's Chosen, there are plenty of directions that the game can take to give Sora some interesting new powers.
Sora's Status as a Keyblade Master
In general, Kingdom Hearts 4 is in the position to do some very interesting things regarding Sora and his abilities. Before KH3, Sora was working towards the Mark of Mastery that would declare him a Keyblade Master as well as unlocking the Power of Waking. Due to Xehanort and Real Organization 13, this didn't happen, but he learned the Power of Waking in KH3 just in time to wake up Ventus. However, it's unclear if this means that Sora's a de facto Keyblade Master or not.
Unfortunately for Sora, it's likely that he hasn't earned the title yet, as Master Yen Sid has made it clear that it can only be done under the tutelage of a proper master. However, this doesn't mean that Sora doesn't have a chance. Interestingly enough, Kingdom Hearts 4 is the start of what's known as the "Lost Masters" arc. While it isn't clear what this title means just yet, it may mean that Sora will gain a powerful teacher soon that helps him finally earn the title.
Kingdom Hearts 4's Worlds Could Teach Sora New Magic
One of the most interesting and exciting things about KH4 so far is that Sora is considered to be in a "fictional" world, or a world based in "unreality." As Sora's friends warned him that saving Kairi might take him to a place in which he couldn't return from, it's highly likely that the Kingdom Key bearer is in an entirely new set of worlds with brand-new rules for him to learn as he goes. This means there might be new magic for him to learn as well.
It's a common trend in Kingdom Hearts, especially the numbered titles, to start Sora from scratch with every game, and there's always a reason for it. KH4 is likely going to be no different, using the new area Sora's found himself in as the answer to why he's forgotten most of his skills. Luckily, Kingdom Hearts 3 gave a good reason as to why Sora picked up on his many skills rather quickly within the first few hours of the game, and Kingdom Hearts 4 is likely to do the same thing, meaning fans shouldn't have to wait too long before using familiar mechanics such as Flowmotion.
There's plenty of room for KH4 to branch out and expand on old mechanics and introduce new ones that help define this next stage of the Kingdom Hearts storyline. It seems very likely that KH4 will certainly introduce some unexpected things, as the last trailer showed Sora using the keychain on his Keyblade like a grappling hook. This expands on the Keyblade transformations introduced in Kingdom Hearts 3 already, and there will likely be many more surprises in the same vein once Kingdom Hearts 4 is in players' hands.
Kingdom Hearts 4 is in development.