Sittin here in the hotel with my room mate on our Advanced Paramedic Course.
Both think it's a great idea, but neither of us (both riders) would suspect it to come apart while we are on scene. With adrenaline flowing we would just end up doing the typical C-spine precautions and slowly take the helmet off... But the idea is great and would make that job way easier.
Scorpion helmets (and possibly others) have an inflatable bag in the top of them that we can inflate with the bulb of our BP cuffs, but something about pushing down on the top of the head where there is a possible skull fracture just doesn't make sense.