I very much would like to see not only small cameos, but some canon story involvement from XV. It would be too much of a good opportunity to pass up when you think about how much both games have in common.
Something along the lines of the Cloud/Sephiroth story elements from KH I and II would be great, and hell, if they did it smartly, I could imagine giving Noctis a keyblade in KH III, I think there needs to be a few more keyblade wielders anyway. To me, Noctis just seems like he fits far too well as a character in the KH world to not be in KH III.
Something along the lines of the Cloud/Sephiroth story elements from KH I and II would be great, and hell, if they did it smartly, I could imagine giving Noctis a keyblade in KH III, I think there needs to be a few more keyblade wielders anyway. To me, Noctis just seems like he fits far too well as a character in the KH world to not be in KH III.