My boarding barn hosted a jumper derby, which is a pretty interesting concept for a horse show. Riders complete a stadium jumping course, then go straight to a compact sort of cross-country course. If multiple riders go clear, they do a jump off that combines jumps from both courses.
Based on my unscientific observation of eventers from around the internet, dressage is everyone’s least favorite phase. There aren’t too many opportunities to do the two jumping phases without that pesky dressage, so this seems like a pretty good idea to me.