The extra steerable axles would not have to be actively controlled. They could just tag along, just like the front axle of a car does when you tow it with a triangular tow bar. Such "passively steered" tag axles are used on some big semis.
But the van's concept is faulty. Imagine driving over a steep hilltop or big speed bump, or thru a sharp dip like some storm drains and driveway entrances. You'd suddenly be sitting on just two of the axles. Ooops!
Good for Halloween parades.