My only concern with this is that RNG behaviors reduce responsiveness. The game can already become quite unresponsive with even simple code solutions. This is partially do to the very large load on the system (some levels use more than 1GB).
Another trade-off might be to reduce damage based on current action (and attack type). For instance, if one is attacking, passive reduction to missiles would be very hard. I’m still toying with the idea, and am researching how to make (and test) my own thang. Hopefully such research will result in ways to add progression (more than just DPS and HP) to gear.
That said, if there is a way to increase responsiveness, reduce load, and provide the RNG behavior, I don’t think this is a bad idea. Again, it might not be as cut and dry as applying it to all shields, but as a progression in the shields gear line. I’m certain that other gear (ahem… gloves…) could benefit from similar perspectives.