Roger that.
A student should not fail the PPB class if they cannot backfin if the instructor unilaterally decides to add it to the curriculum.
To do so would be a standards violation for that agency.
Other agencies would allow/support an instructor to require that and fail a student who was not able. Though I don't like to use the word fail. Rather, I believe in breaking up con ed with teaching (which includes feedback for students attempting skills), a break where the student practice until they master the skill, and then an evalution to ensure that skills have been mastered. I do understand this doesn't work in vacation spots where students are there for a short period of time. They want a card for their efforts, even if their efforts fall short. That's a business reality.
To me it is about sensible additions. For earlier courses, adding (or interpreting) things for improved control (finning, ascents, descents).
Once those items are mastered, then add some sort of task loading. Say a deep diver course with deploying a DSMB from depth and stopping at 10 foot intervals.
I'm on the fence about anything additional to that. I've stopped teaching deep courses due to my awareness of gas density issues, I need to have a conversation with higher ups on how to address that. Obviously I'm not going to create an emergency, or force my students to fin really hard to exert themselves and give them a task, at 130 feet and say back at the surface "see how hard it is to deal with that when you are narced out of your mind due to increased CO2 generation?" But I would like someway to address gas density issues at depth when dealing with emergencies. But that is a
long conversation that I will have in the future with not just my agency, but other experts as well. I will NOT just be a cowboy and put my students at risk. Whatever I do (if I do anything at all), it will be safe, approved by my agency, and vetted.