I get the jaw locking issue from deepthroating or from holding my head at weird angles. It’s a shame because I love sucking dick and it’s one of the few sexual activities I can do reliably without discomfort, but generally I just suck the head. Perhaps a system of restraints, like a dental gag or ring gag + rope, would solve the issue. I’ve never used an open-mouth gag but it’s definitely on my wishlist.