shield V2 (link)
This page could/should be used to talk over what the engineer could stand to gain from the idea in the main link aswell as possible traits and uses for the idea.
lets not let the cool idea die just yet
One possible idea is a trait that places a little gadget on the top of the shield and as you block it shoots at the enemies infront of you, could be classed as a turret and benefit from other Invention traits.