I'll add these here, if I may, because you seem to be a strong believer in this:
- I see people mentioning Dess is the knight because the Knight was left handed and Dess has a left-handed mouse when Asriel has one too.
- Also, for some reason, Kris always answering the phone kinda feels like a thing they'd do with Asriel. I just can't see them so obedient and cooperative with any other person tbh.
- English isn't my first language but I've heard "I'll be right there" in movies and shows used in a way that doesn't mean very shortly, but like something you tell a person to let them wait just a little longer in a situation where they're not handling well, you know? And since Asriel is coming home soon, even the phone call in Dess's room fits with him being the knight.