nonviolent de-escalation can be a part of a comprehensive self defense program....in theory. How exactly do you train and measure it though?
With the caveat that I haven't done any such training myself, I'm reminded of my wilderness EMT training. Rather than simply showing us how to splint a fractured femur and have us practice, our instructors created deliberately stressful situations to make us deal with all the other things that could happen: panicking patients, interfering bystanders, rain, snow, hail. You're not fixing a broken car, you're dealing with other human beings and their reaction to the situation, and your ability to manage the human part of it will greatly influence the outcome of the "broken car" part of it. It was very hard training, but very effective, as I found when I had to use my training for real. How you measure it? I have no idea.