Trucks and trains are often not sprung, and can benefit from lighter, smaller,more efficient hub motors. Cooling is easier when the whole motor is moving through the air.
More than the body needs to weigh enough, you need a proper center of gravity via weight distribution or you're simply going to tilt the thing over and wreck everything when you lift an object (source: have multiple sit/stand/clamp lift certifications.)
"Size matters, in forklifts, which need to maneuver in tight spaces."
That's why we made the reach forklift, which is operated while standing up. Half the footprint of a traditional forklift with the ability to reach out across a shelf to pick up a pallet.
Where this will make even more sense is for driving conveyor belts on assembly lines. You'll save more power there in a manufacturing warehouse environment than you typically will switching your entire forklift fleet over to these new motors.
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.678...
https://en.wikipedia.org/wiki/MagneRide
https://www.youtube.com/watch?v=hiaMpG4Y640
Further, on newer vehicles with the trend of 20inch+ rims, that is already 60-90+lbs (27-40+kg) of unsprung weight per wheel with tire. There is certainly room there for improvement to offset at least some of the motor weight.
Would have to know how much their in-wheel models would actually weigh though to determine beyond speculation if it could be reasonably compensated for in a highway vehicle.