Ripe for abuse, both because it's easy to fake a doctor's note and because there are too many doctors who will just give the patient what they want, whether they really need the specific accommodation or not.A need for a particular accommodation. Most likely from a doctor, or maybe certain therapists.
Plus, that doesn't necessarily mean (not sure if this is where you were going) that the guest would still need a DAS. A doctor could legit write a note saying that the guest can't wait in a line longer than 15 minutes. Well, there are other accommodations for that.