I have been looking for something like this idea. There could be different vehicle classes (stock vs. lightly modified vs. heavily modified), but I don't actually think that's completely necessary. Overlanding has created a never-ending series of compromises with my rig. ATs or MTs? 3.73 gears, 5.13s, or something in between? Trailer, roof rack, or neither?
The point is, I have a two door Jeep and would love to "race" with 4Runners, Land Cruisers, F350 Earthroamers, motorcycles or whatever. I know my disadvantages (fuel capacity, highway speeds, packing/unpacking my ground tent, payload--though I don't pack a lot). But I can also navigate tight trails/switchbacks, climb rocks, and finish technical terrain faster and easier than many rigs lugging 10,000lbs of gear around.
For me, the route would have to have to be as diverse as overlanding. I could imagine a route from CO to southern Cali. Some mountain passes, lockheart basin down to the southern Utah traverse. Finishing with the Mojave, or maybe even heading down into Baja. It would also be great to include other skills in portions of the race, like route-finding/navigation, camping in areas of varying climate/harshness/amenities, and requirements for days in a row of being completely self-sustained.
Points-off or disqualification for violating Leave No Trace.