Bracing will change the behaviour of the crumple zones. Whether that change is a good thing or a bad thing, would require substantial effort to establish. Given that modern vehicle bodyshells are already highly engineered with regards to crash structures, my money would be on the effect being bad.
The holes are almost certainly to control where the beams start deforming when subjected to crash forces (acting as a column). Crash structures very commonly have designed-in holes, folds, bends, etc., in order to control where and how the structure deforms.
And now for the big question ... Why are you interested in stiffening in the manner shown? All it's going to do during normal driving is to add weight to both ends of the vehicle (bad) and stiffen the bumper from moving sideways (irrelevant for any purpose that I can see). The places where stiffness matters are all between the wheels. Anything hanging out over the ends beyond where the suspension attaches to the chassis, doesn't matter so much ... except for crash structures.
