Re: Box Jumps?
I question whether Julie's injury was due in part to the combination of high rep box jump overs following a run on the True Form runner which may have taxed all the athletes' achilles in a different way than their bodies were used to working. But regardless, I tend to think safety is likely a consideration as the original poster suggested. There are way too many athletes in the Open who would be ill advised to attempt 20" for women and 24" inch for men high rep plyometric box jumps. It is a big risk if you are not used to doing them... ...and your achilles isn't going to give you warning before it snaps--it is just going to go without warning. I'm 47 and limit plyo box jumps to lower boxes, 12" or lower, except on occasion I've done some low rep efforts up to a 20" box. It just isn't worth the risk given my beat up body.
As Victor points out the burpee in the middle would be a solution, which get rid of the plyo aspect.
Once you get past the Open, and you are dealing with Regionals or Games athletes, I tend to think that is a different story (at least in the individual ranks as opposed to teams or Masters). Expecting plyo box jumps out of those athletes is a little different (just maybe not following a run on the True Form until it is a commonly used apparatus and athletes have experience training with it.