Well ideally there wouldn't be sequels.
Hence why I'd hope that if there WERE, they'd be handheld. Or smaller teams at least. I mean, yeah, Nomura's working on both this AND KH3, but it's two studios. XV is the team that made KH1 and 2, and KH3 is the Osaka team, more officially known as Production Development Department 5 of Square Enix, or PDD5. They're the ones who made BBS and 3D.
So yeah, even though two games are being made right now (likely more), there's more than enough attention going to each of them. Separate departments, ya know.