I think I just realized the #1 thing I'd change about scuba-training.
Cut out the Middle-Man.
Based on some preliminary research, it appears about half the expense of a dive-class goes to the training-agency for "e-learning materials." In my experience, these "e-learning materials" are by far the worst part of any dive-class in terms of being extremely boring and not updated very often. That leaves the remaining half to be split between the dive-shop, instructors, and material-expenses (pool, equipment, tank-fills).
To be clear, I understand the e-learning saves instructor's time, and lets them focus on hands-on, and that agencies provide some level of (debatable) quality control.
There are a few ways to approach this, but I think a decent start would be tutoring. Sure, you don't get a certification card, but I personally don't take classes for some certification card or achievement. Perhaps have a session focused on finning techniques, bouyancy, or other similar specific skills. You could even do things like bi-weekly or weekly group classes, where you go over random intermediate skills. Perhaps offer enough of a discount for the people who show up to every class, to incentivize attendance even for those who already know the skills covered. Instructors could probably make more money, while students are also paying less.
Anyway, it's just an idea, perhaps other people can build on it.