Thinking in terms of, "Who would have the most interesting interactions with Sora or Riku (or Sora/Riku types)?", even if they started writing these characters with more care, the cast we have still doesn't feel like enough. Overall, I like them, but it's a lot of stiffs, and even the edgelords aren't edgy enough. There really needs to be a jock character to get in some faces and shake things up. Even better, a KH character who is a complete freak. Or a ditzy hippie. Or a creepy clown. I know Nomura has certain types that he likes, but a fuller garden of personalities would help his favorites shine by giving them a more vibrant cast to reflect off of. Even if they fully integrated Disney and FF into the story, which they should, I still think we need new blood. They added a bunch of new guys to Dark Road, but none of them seem to have that spark I'm looking for, from what we have to go off of. These are essentially games about wizards, and wizards should be weeeeird.
I think we'll get there eventually, but I'd like to see family finally confronted. We should meet the parents. Get a little insight into Riku's home life and why he's got an edge.
I want to see an adult who knows what they're doing. If Sora (or whoever) had a meaningful relationship with a mentor or a parent, there's just so much emotion that could be explored. If we are headed to a "realer" chapter of Kingdom Hearts, I'd hope we're rooted in a more fleshed-out world and community, where your adventure is more than a Disney daydream away from home. Or, if they wanna keep things abstract, cool, just feature at least one really solid relationship dynamic that pulses through the whole story.
I think it's time to bump the romance up, to match the many Disney worlds with all their love stories. There has got to be a BALL in a KH. Where you dress up and go on a date, and then yeah of course some magical mayhem will ensue. And ideally, you'd get to pick your date.