I don't think it's a terrible idea, but I also don't think it will impact fatalities much. AEDs help with a cardiac-based cause of collapse, but when it is a cessation of heartrate because of a lack of oxygen/ventilation, it won't really help, only establishing breathing will, and the HR typically comes back naturally with that.
I work with babies and their causes of cardiac arrest are almost always respiratory in nature, so I can count on one hand the number of babies I've seen needing defibrillation, additionally, unlike what they show in TV shows, defib will not restart a heart. Epinephrine will.
Since many causes of cardiac arrest in diving I think are respiratory in etiology, I wouldn't think it would make a huge difference. Additionally, the time it's going to take to get to an advanced care facility, if your primary pathology is cardiac, is going to be pretty prohibitive. It's unfortunate, but if you have a serious arrhythmia somewhere far from advanced medical care, your outcome is unlikely to be good.