The Mahi I mentioned earlier is a boat in 95' of water. I did the first one from the top deck, and then worked my way down. It was the first thing I had to do for my DM course, be able to do a CESA from the deepest depth I was likely to guide people.
I don't think a typical diver can do it slowly, exhaling continously, without practice. I could not, the first couple of times from 60 feet. Thus I think everyone should practice it, far more often than the typical skills that get suggested for practice (air sharing, no mask swimming)
On the other hand, in the old days every one could though, they did not worry about ascent rate, nor do I think someone who is out of air should worry about ascent rate. So finding someone who can do it should be no harder than finding someone certfied in the old days when ditch and dons were part of OW certifications.
On the other hand, with taking advantage of the drop in ambient and breathing from the 'empty' tank, and not worrying about ascent, I imagine a fair number of people can still do it, since there are a some number of people who run out of air and not that many that die from it, though most don't have to demonstrate it from any significant depth in training.
---------- Post added July 7th, 2014 at 10:16 AM ----------
If fast ascents from 100' killed people, there'd be a ton of tourists dead every year, and all of us who dove before computers would also be dead. Stuck inflators, failure to be able to dump properly, lost weight belts, make lots of tourist divers pop from 70' feet.
Breath hold ascents are deadly. Fast ascents are not good, but not deadly.