Not sure, but I seem to recall Captain Cuthbert mentioned cold plates somewhere in regards to his truck Shachagra. I do recall he used a small fridge and a drop-in freezer - sailboat style. Not surprising considering his degree in naval architecture and all of the sailboat style details he used in his truck.
The issue with the engine driven compressor is that of complexity. Quite a few overland campervans use diesel fired hydronic units to both heat the cabin and hot water and also pre-heat the main engine. These are tied into the engine's cooling system. This also allows the main engine to heat the system.
With a cooling compressor driven from the engine, you now have to add the compressor - or 2nd compressor if there is one there already for the a/c - and tie that into the camper cabin.
More complexity equal more potential points of failure.
With the advent of the Danfoss variable speed DC compressor, many 12v (and 24v) refrigerators (and a/c systems) are quite efficient electrically, so there isn't much benefit gained from extra complexity.
Cold plate technology is however becoming more popular I think. Novakool has been doing it for years, and I think they have a fridge designed for off-grid solar which is a standard Danfoss compressor fridge with cold plates added, and which detects when the battery bank reaches full charge and then uses excess solar wattage to power up the cold plates. This makes the already efficient intermittent compressor cooling run at an even lower duty cycle by storing "extra" solar power in the cold plates.
Current: 76 E-250, bubble-top, self-contained|couple of old Yamaha enduros
Previous wheelers: 41 Willys|78 FJ40|78 Bronco|84 Bronco|74 Ramcharger|78 Ramcharger|79 D150 PowerWagon|77 D100|79 D400 dually, converted to 4WD, utility bed, 10' Lance|75 Westy|69 Scout, RHD|bunch of others|bunch of bikes|couple of boats|couple of motorhomes|blah blah|so what|not my idea|just doin' what I'm told|wank wank|this space for rent|candy is dandy|but liquor is quicker