What if they could connect this with armors? And basically make them the new limit forms?
Ventus, Roxas and Xion are all in Sora's Heart. So when you choose the respective limit form Sora would be covered in Ven's armor with his stance and battlestyle or be covered with Xion's armor (Final Boss of Days) with her own battlestyle and the same thing with Roxas too. Although they would have to create an armor for Roxas, maybe similar to the Nobodies he commanded when he was in Org. XIII?
Edit: Basically it's still Sora but with different armors instead of switching bodies completely.