Once they have the foot in the door and can "control the size" (presumably on "big" vehicles first), watch them start tightening the regs to require vehicle sizes that are smaller, and smaller, and smaller, until...?
What I get from this is they want to control the shape of the vehicles. That shape exists to stuff all the things under the hood there, or to provide a more aerodynamic profile to get increased mileage, cooling for the engine, and better mileage. As far as vehicles being tall, well, some are by virtue of greater ground clearance--a seasonal necessity in some places, to avoid getting stuck. Like EVs, in the unforgiving winter clime here, close to the ground just translates to 'not going anywhere'--AKA: a hazard to navigation.
I 'get' that taller, more 'monolithic' vehicles have a different impact profile on a pedestrian than small cars, but it seems the bottom line here is to not walk in the road, and you won't get hit. (Face traffic, wear light, bright, or reflective garments, especially at night, don't walk out from behind obstacles, look both ways before crossing, etc. PUT THE PHONE IN YOUR POCKET!)