>>6593559This is a pretty good setup. I would also add in swivels at mid-elbow and mid-knee, which Bandai recently used on Tiger Mask and I think the wrestling figures as well. Those things are unobtrusive and work great. And no, they aren't redundant due to the bicep swivel--sometimes characters with oddly shaped/muscular biceps cannot rotate them when held close to the body, or big pecs/boobs block their movement. Swivel double elbows solve this neatly.
If we were REALLY going for perfection, I'd also try to add the interesting hip joints from Busou Shinki, which work kind of like a car door hinge, and allow for extremely high leg raises. So you can do poses like hugging their knees to their chests. I'm aware that implementing this might cause other problems though. We'd probably need to re-engineer a new solution.