With the caveat that many people may want no changes, I thought I'd bring this up.
First, the concussion stuff is not going away. Without fundamental changes, I don't see the NFL becoming safer in that regard, and the dangers I think are real. However, some change in this regard would obviously be welcome.
But, second, I think most fans hate seeing their favorite players miss games due to injury. I don't think you can legislate all injuries out of the game, but I think there are probably some steps the league could take.
There are often unintended consequences, but who knows.
1. More referees.
2. More things eligible for replay.
3. Refs can call for replay...certain number per game maybe? Mostly, I hate how there is often an obvious player down or incomplete then dropped ball, but the refs let the play go on because they've been instructed to err on the side of that since they can undo a fumble, but can't "re-do" a fumble that they blew dead. Some of that is better with auto check on scores and turnovers, but maybe they could have a certain number.
4. I'd change tackling. I'd only allow pushing with hands (if trying to force out of bounds), and in field of play, I'd only allow grabbing (hand on jersey, eg), tripping (hand to leg), and wrapping up. No head spearing at all, no shoulder tackling.
5. Something needs to change about quarterbacks. I think they are protected enough as it is (at least in the rulebooks) and offenses are potent enough as it is. The problem, I think, is terrible enforcement and consistency, which might be helped with more refs. But I personally get annoyed at the balance between trying to call roughing the passer, but allow the play to continue...I don't think you can have both. I hate seeing defensive players have a qb, then kind of hold up because they are afraid of a penalty, then the qb breaks free and makes a throw, etc.
5a. I'd allow refs to review roughing penalties and/or coaches. Get them right.
5b. Sometimes, I think refs are hesitant to call roughing passer penalties because they are too extreme. 15 yds, auto 1st down. So I'd have 2 tiers. 15 yds auto 1st for real blatant ones, then 5 yds, replay the down for more minor, technical ones, but call them more often. Such as, any contact to quarterback's head or below knees, etc. I think they would call it more if it wasn't such a game changing penalty, and that might keep defensive players from constantly upping the ante on what they can get away with.
5c. As a trade off, I'd actually blow the whistle faster on qbs being down. My philosophy is, if you are going to be so protected by the rules, you don't get to also extend plays where a less cautious defensive player would probably have gotten you already.
6. In general, I'd penalize piling on more consistently, and maybe even make gang tackling illegal, but again, with the offset of blowing the whistle quicker.