I'm just now realizing that Auron is the perfect fit for the person that Donald and Goofy are looking for, and not Hades:
• Auron has been dead before
• Auron knows of being dead and traveling from one world (Zanarkland) to another
Other than that, it'd be the perfect utilization of FINAL FANTASY property inside kINGDOM HEARTS, seeing as how the lack of presence in vanilla KHIII was mentioned.
And the devs are taking into consideration feedback from the fandom, what with Reaction Commands making a comeback precisely because of that.
By the way, according to KINGDOM HEARTS Twitter, Sigurd, or however his name is spelled, si the narrator for both trailers.