Not to hijack the thread and turn it into a discussion specifically about how to create a training hierarchy, but I think this type of format (with some tweaking of course) is what would make the sport more appealing. As a kid, I don't think my parents would have pulled the trigger on the cost of my OW course if the education had seemed endless. All that was offered was OW, AOW, Night, Deep, Ice, Wreck, DM, Instructor. But, knowing what I know now, quality education makes a huge difference. We need a little more experience from the instructors, a little more quality-control in pro level training, and a little less superfluous coaxing to put money into the sport by students who truly want and believe they are getting good value for the dollar. My girlfriend is a figure skating coach and they are doing it mostly right in that world ... except for the point system in competition which is way off topic.
Diving should be made affordable and fun for the OW diver and at most would require just one class. Some would be happy at level 2. After that the truly dedicated would still seek out training to enhance adventure.
No C-card for a DSD, Resort Diver, or any training that isn't a full cert. Freediving no C-cards.
Scuba Diver Level 1: OW + Surface Rescues + Deep + Night + Advanced Navigation + DSMB + Primary Reel
Scuba Diver Level 2: Intro to Tech + Drysuit + Nitrox + Doubles + U/W Rescues + Dive Leadership (certified assistant/class & pool instructor)
Scuba Diver Level 3: Divemaster (also must be certified lifeguard & EMT with 100 dives)
Scuba Diver Level 4: Open Water Instructor (must have 500 dives)
Technical Diver Level 1: Advanced Nitrox + Hyperoxic Trimix with 1 Deco Bottle to 150
Technical Diver Level 2: Extended Range + Normoxic Trimix with 2 Deco Bottles to 200
Technical Diver Level 3: Hypoxic Trimix with Multiple Deco Bottles to 300+
Technical Diver Level 4: Technical Diving Instructor (OW instructor with 300 dives above level 1)
Ice Diver Level 1: Diver
Ice Diver Level 2: Instructor (OW instructor with 100 ice dives)
Wreck Diver Level 1: Penetration Diver
Wreck Diver Level 2: Instructor (OW instructor with 100 wreck penetration dives)
Cave Diver Level 1: Full Cave Diver
Cave Diver Level 2: Stage, DPV, Survey, Rescue/Recovery
Cave Diver Level 3: Cave Instructor (OW instructor with 300 dives above level 1)
Rebreathers (unit specific training from manufacturer endorsed instructor could issue card through his/her affiliated agency)