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Excellent question. As you say, the induced draft arrangement is very common in cooling towers with large fans and small fans. Normally in this arrangement, the motor is outside the fan stack in the cooler air. You do not mention how the fans and gearboxes will be accessed in this new arrangement. It is not obvious.
In the normal cooling tower, the structural beams are narrow and the steel support is either a round pipe or narrow steel I beams. In concrete framed towers the fan blades are some times too close to the wider beams that are in a concrete tower and cause a pulsation/vibration due to aerodynamics of the airflow passing these beams. The large beams in a motor bridge could cause this same issue.
Also, the air temperature that would be flowing over the gear reducer and motor may be too warm to properly cool the gear and fan.
The benefits of this arrangement may be very interesting. The exit velocity from the fan stacks will be much higher than a normal A Frame ACC and I would assume there is no real perimeter walls. Thus, recirculation should be reduced. Air flow into the fans should be less effected by wind, thus the flow will be more uniform and will likely reduce blade stress.
Hope this helps; Gary Mirsky