I don't think anyone would object to Hayden returning, but we know that they're not going to divide the roles. SE very clearly wants to maintain that consistency with Kairi and Xion having the same voice; that's why we only ever have Hayden OR Alyson voicing them, never both in one game.
Hayden voiced Kairi and Xion in BBS and 3D.
Alyson voiced Kairi and Xion in Days and KH3.
If Kairi and Xion were to appear in future games together, they would continue to share a single actor, whoever that may be for the project in question.