I know this is just my observations and should be taken lightly but in my opinion...
as far as headgear goes. standard rugby headgear isn't very thick and doesn't dampen impact very much.
I think thicker headgear like what is used in boxing would help a bit more in some (but not all) situations.
The problem with its use in boxing is that it just allows boxers to take more hits, so the end result is the same or worse.
Rugby has a major problem. Its really interesting how the problem seems to be much worse for Union than League. And rugby union referees are far more strict on contact to the head than league refs. It suggests that the type and frequency of contact that occurs in union is more detrimental. That may not always be direct head contact either... Collisions that contribute to concussion don't need to involve head contact. It just requires sharp acceleration or deceleration of the head.
Funny the two worst head knocks I took as a player which gave me concussion. one was contact with the ground and the other was a head clash with a team mate as we both tackled the same person. But thats fairly meaningless.
The modern problem is that modern athletes are bigger and far more physical. The contacts have far more energy and are a lot more frequent. But there is no known way to train or prepare the brain for the increased energy and frequency of collisions in Rugby.
Hopefully Lambie comes back well, he's a class act.