A. you have no idea how many c-cards I have. You'd be shocked at how few there are.
B. I have no desire to take cameras into caves and do the post processing because I am too busy actually enjoying the dive and have no means to profit from it. If I want to see it again, I go back to that passage. Toddy has a lot to profit from videos like that, as do you. Which btw, your youtube channel is actually really interesting and appreciate it as a learning tool when teaching.
C. The lack of video footage has no bearing on me actually doing those dives or not. I wish I was doing exploration dives in Mexico on the regular, but I do plenty of true sidemount only dives in Florida.
D. I have been sidemount diving for close to a decade, and been sidemount cave diving since 2010, so I have been at it for a while, and yes I have dove sidemount with a hard backplate and enjoyed it in open water.
Now, if you read my first comments. I have no issue with this for caves that you are not planning on going into any restrictions. 99.9% of sidemount cave divers fit into this category and obviously all open water sidemount divers. The system is an evolution of the Nomad that Dive Rite developed 20 ish years ago when they first took a rec wing and stuck it under a transpac. For the cold water where you live, that is very advantageous so you can take advantage of the negative buoyancy. Where I dive in Florida, we are usually focused on getting weight off of our body, and due to the essential requirement of using steel tanks because of how deep our caves are, we don't usually wear any lead, even with all fabric sidemount rigs. The shallow cave depth, combined with wetsuits, combined with aluminum 80's as cylinders go to how small of a profile that rig can attain because there is almost no air in the wing. It looks the same as a Dive Rite Nomad XT in the same type of environment, just without any lead strapped to it. Great, for that environment.
I could not safely dive it in many of the environments I have dove in, and I don't take my Nomad XT into those environments. I take my Hollis Katana which has a smooth back profile and nothing to stick up to get caught on the ceiling. Divers have gotten stuck using hard backplates in sidemount, it is nothing new, and it is very real. Those divers no longer use hard backplates for their true sidemount diving.
I have much stronger opinions about the choice of hose configuration for the regulators and plan to switch tanks than I do about the choice of a hard backplate.