The FDX Suppression system mayl not work on a 747, the reason is that a 744, 742 and even the 777F do not use containers (typically). Each position is loose loaded to a specific dimension on a cookie sheet wrapped in plastic and secured with netting to the sheet. An injection system would simply flood a single box or several boxes but would not flood the immediate area surrounding the cargo in that position since no containment exists for that cargo.
I could see foam being used, but without knowing the specifics of the volume of foam that can be produced on board it may not be practical from a size/weight standpoint.