I've had this idea for a while. It would be mandatory to have transponders to be able to do this type of racing. This kind of builds off what they do in timed enduros but for motocross. This is just a concept, haven't worked out the details.
What if an organizer had a two hour rotation of motos/races. Bike Bike A/B race, Big Bike C race, Big Bike Open, Supermini race, 85cc race, 65cc race, 50cc race, ATV race, 30+ race, something like that, haven't worked out he details. Max of 40 racers in a moto. The two hour rotation of classes would start at 9am, 11am, 1pm, 3pm, 5 pm and each race would be 15 mins (again haven't ran the math yet, just a concept). A racer would sign up for a class (normal motocross classes or even more classes) and then reserve a spot in whatever 2 races they would like to be in (for the two moto format). So for example a racer could sign up for the 450 B class and the Collegeboy class and then reserve the Bike Bike A/B race at 9 am and 11 am for the 450 B; then the Big Bike Open race 9 am and 11 am for Collegeboy. The rider would race both the motos and his overall time would dictate his overall finish. Then the rider is done. At the end of the day, the final results would be posted online and an award would be mailed.
This would be attempting to do a couple of things. Larger gates... by making all classes ride together but scored separately it gives the environment of better racing. The ability to race when it's convenient to the rider... I'm not a morning person, I like to ride in the evening, if you told me I could show up and still compete with other riders (maybe not directly on the gate but on paper) and get my motos in at 3 pm and 5 pm, that would help with coordinating my weekends. Gets rid of the long days but the same riding time... show up at 9 am, out by noon (possibly), you could race 2-6 motos within 3 hours. More classes... same overall race time, but opportunity for more classes.
Some of the challenges. Practice... would have to be shortened greatly, maybe just a hot lap before the motos. Limited space for racing... each race would be limited to 40 man gates, I haven't ran the math, but taking all big bike classes and pulling them into a open type class, could be a problem. Open type racing... Not all riders are created equal, racing with all levels of riders or ages could be a issue. The motos would have to be equal race tracks... you would want the race tracks to be similar throughout the day to hold up the integrity of the overall times (possibly have to have more designated track maintenance).
Again.. just a concept. Haven't worked out the details. With more technology coming, we should be able to have increased convenience for racers. Just trying to think outside the box.