The problem with showjumping is it doesn't mimic the original concept of the sport, i.e a soldier behind enemy lines commandeering an unfamiliar horse. That soldier is hardly going to take said horse and go around a course of jumps on a sand ring. He's going to take off like a bat out of hell across country, probably jump some obstacles, maybe negotiate some other scenarios like open a gate while on horseback, go down steep inclines, go through water etc.
Maybe if the riding portion was a modified XC course, with alternate routes that incurred time penalties for those riders not as confident in their or the horse's ability to jump some of the obstacles. Throw in a few things that test horsemanship like having to back your way through a narrow chute. Borrow some elements from those Portuguese working equitation speed tests.... http://www.youtube.com/watch?v=5895K-Xjupk
I acknowledge that the fencing probably has to be a stand alone test. But maybe something like this, do the fencing first. Then use the standings to have staggered start times (as they do now in for the running/shooting part) for a ridden XC/horsemanship test. Then jump off your horse, pull off your boots, breeches and helmet and jump into the water for the swimming portion. Then out of the water and put on a pair of running shoes and straight into the running/shooting combined.
Now that would be exciting.
Granted you'd have to work out some kinks like multiple horses/riders on course at the same time, esp if they were approaching the same obstacle. But that might even add to the excitement.