Cavern has, by and large, by most agencies, been moving in the direction of being more of a recreational-level safety class.
This rather than a strict part of the curriculum of course progression many overhead training agencies think of cavern/cave diving as a two-step progression.
As do I. The overwhelming majority of the time I tend to teach cavern and Intro (through the TDI standards, cavern is still a prerequisite) as a single class.
To my way of thinking there is overhead and there is not-overhead. If you are not in overhead you are open water diving and you have a LOT of wiggle room. Because the surface is always available to you. When you are in overhead, by definition, it is not. Ergo (again, to my way of thinking) it is wisest to be fully equipped in redundant equipment and trained in both its use and the use of self- and team-rescue techniques to deal with overhead emergencies.
Yes, I do believe even divers untrained for the overhead can safely execute dives into the cavern zone. Guided. Supervised. Well-briefed and conservatively planned. The safety record of the guided cavern dives in this area of the world demonstrate this. (Can it get better and safer? Obviously. As can any endeavour. And organisations like CREER are actively working to make it so.)
Can a cavern-trained diver safely execute an unsupervised cavern dive? I don't see any reasoning why not. What's more, it makes a great intermediate class for folks who might not yet be confident in their skills, comfortable with their gear, or feel as stable and in control of their buoyancy and trim as they might like before going into an Intro class. Something like "Intro to Intro" or "Cave Primer."
But. The limitations placed on a cavern dive in terms of penetration distance, depth limits, gas usage limits, etc... it's not like these are going to be terribly long dives. Seems like it is just as much a teaser for overhead diving as anything.
So I like the two step progression; at least for the folks who are stable as a table, are as comfortable in their harness as an old pair of slippers, and suchlike. If we're going to go into overhead... let's go into overhead.
For all that said: It's been a weird couple of weeks. Because I'm working someone through the second of two back-to-back stand-alone cavern courses.
Time-wise (and relevancy-wise) t's hard for me not to geek out about hydro-geology as enthusiastically as I do during an Intro or Full class.
I dunno. What do you think? I prefer the two-step progression. But that's me. It doesn't make it right. Or wrong. It's just how I tend to think about things.