Mine is on pre-order, and hope to get it soon. I don't mind the gap as shown above. My 7D l-plate doesn't have the gap, but to use the camera in portrait orientation, I have to loosen the mounting screw and slide the l-plate about 5mm "IF" I want to use a remote trigger. This means I have to carry the allen key.
As shown in the other view orientations of the 5D3 l-plate, the gap means there is no need for any l-plate adjustment when using a remote trigger. I think they have thought this through quite well.
I'm sure I recall seeing an image that showed the port cover being able to rotate through the gap to stop it being pinched or caught up in the clamp too (maybe they updated their images with the laser etched versions), so I thought it was a functional gap.