The first thing we need to make clear is that "severe, incurable, and unbearable" does not necessarily mean terminal or even physical pain. Plenty of psychiatric conditions often accompanying significant trauma are severe, incurable, and unbearable. But they're not terminal (except by suicide), and the reason they're incurable is because we know fuck all about psychic damage, and some might argue that if you've made it this far without killing yourself then it's de-facto bearable. And yet they definitely qualify unless the law specifically says that they don't, because "deemed unbearable by the patient" is not the same as definitively unbearable.
The biggest flaw I see in the model is if there's no significant determination of qualifications for whether a particular doctor should be allowed to approve the request (e.g. some might demand that the doctors be trained in appropriate specialties and have detailed knowledge of your history and situation), or whether you can ask 100 doctors who say no until you find 2 who say yes. I've seen firsthand that systems which don't mandate strict selection criteria create additional strife.
I think that fundamentally one has to decide whether a person gets to just say "I want to die" one day and forget that there are doctors involved. Because believe me there are many scenarios that basically feel that way to friends and family. Many people with trauma are extremely suicidal but also scared of the process. Do we establish a structure that makes it easy to get help dying or do we want to instead mandate state resources for helping them stay alive? For a lot of people the answer is not so clear _even_ when people want to be ok with letting people make their own choices.
[edit: sorry for using british slang, drive-by commenter. "fuck all" does indeed mean "nothing"]