I agree that we really need this. I played OoT3d recently and the sword button was B and it was just so... so weird. I was literally sitting there yelling "WHY". B is never for attacks, it's for jumps or items if there's no jumps. I've forgotten what the B button is in Botw.
I've thrown this theory around a ton already but I bet anything Fi will be in this game in some form.
Additionally, I don't think Ganoncorpse is going to be the main villian. Maybe a side villian, but having him as the big bad feels too obvious considering how many details they've been hiding.