If I have understood this correctly, in reverse acting gate valves, you pull the plug up to close the valve. Gate down = open valve.
What are the benefits of such a design?
Maybe it means air-to-open rather then air-to-close? This would be fail safe in some instances when and if you loose signal and/or air supply and it presnts a hazard if valve remains open.
Reverse acting usually refers to actuation and not valve design.  The design you suppose would have the valve stem in the main flow area when the valve would be open, and this would not be practical.
I would think that in a situation of a dirty service this would be good as the pocket below the gate would be 'full' of the gate in the open and flowing condition.  Because of this, the pocket would not be subject to filling up with debris that could cause the valve from fully closing.

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