The BOG would be run through at about 15km/h (4.2m/s) which is a good walking pace. That is a rate of about 1 axle per second. A bogie exchange might be one bogies in say 3 minutes. A container transfer might be 3 minutes each.
The cost of each Gauge Change bogie is unknown at present, but developmental costs would average out before long.
Areas to store containers would become unnecessary.
Transshipment capacity doubles at Kazakh border rail terminal
So long as the Gauge of the Gauge Change kit avoid narrow ones like 1000mm and 1067mm there is adequate space between the wheels of 1435mm and 1520mm gauges for brakes and traction motors.
See Video GC