Alternately (although this would really change the sport) you could look at moving away from mounting the head-protection on the head. Instead you mount a cage

Alternately (although this would really change the sport) you could look at moving away from mounting the head-protection on the head. Instead you mount a cage on the chest and shoulder pads - like a spinal recovery halo brace without the skull drills. A wearable rollcage. It would look absurd and reduce their mobility, but it would shift the impacts from the head to the torso.