With how massive the wheels and tires are, maybe hub motors with batteries packed in their centers could work. I don't get the impression that monster trucks strive to minimize unsprung weight, the tires are wrecking balls.
You wouldn't need huge battery life for a 15 minute performance, so shaving off battery weight might just work. What most people go to see is airborne jumps rather than crushing things hence need for low weight.
IIRC the rubber tires weigh 1000+lbs each, I wonder if the tires could be implemented differently using lightweight materials shifting their weight budget into hubmotor+battery.
Tires are consumable so you're unlikely to see monster truck teams adopt anything too exotic for cost reasons unless there's a huge performance improvement to go with it.