Just checked your last link, I like the way it could be retro fitted to existing targets.
I agree there is nothing wrong with the current design so long as it's well maintained.
But your idea gives great flexibility with the ability to swap out both kill zone size and shape, also no one could complain about seeing daylight around the paddle. My one doubt about this design is jamming, the further away from the centre of kill you hit, the more chance of the kill zone shaft tilting and wedging in the brass bush. If this idea was built into a target from the ground up, I can't fault it.