I still think the key to curtailing concussions, CTE, etc., lies in the infallibility of the protective equipment.
Defenders from the NFL down to practically Youth Football go for "kill shots" every chance they get (see: Burfict, etc.). That's what gets them on SportsCenter, etc., including whatever renegade videos the NFL chooses to "see no evil." They have no fear of laying a ballcarrier out because they know that their headgear and shoulder pads are far more of a missile than the BC's head or chin.
If the equipment had restrictions on surviving an impact -- such as what the PGA imposes on the tour golf ball -- then all tacklers would think twice about going for kill shots at every chance; their own headgear might be the one to cave-in on a helmet-to-helmet hit.
At the end of the day, I'm amazed that the NFLPA has never drawn a line in the sand on one of its own being laid- out by another of its own.