Sorry, Ralph, none of that has been proven, results are anecdotal at best.
Both the NFL and the NCAA have not reduced the number of returns by moving up the kickoff spot. What they have done is added more hang time to kicks as some coaches want kickers to kick the ball as high as possible and drop it on the 5. This actually creates MORE contact on kickoffs.
As for the scrimmage/exhibition game issue, we have a pre-season game on Thursday, and all kicks are live. Some scrimmages here have live kicks, some do not. The coaches that don't want kicks live in scrimmages are they ones that don't teach special teams until last, and spend far too little time on it. I want live kicks in every scrimmage and preseason game, because I know we are prepared for it. Our opponent on Thursday wants live kicks, but doesn't want his QB tackled. Does that mean QBs are more delicate, and we should create even more rules protecting them individually? No, it means this guy has hasn't prepared his QB on how to play properly.
Requiring 4 players on either side of the kicker will not reduce the number of onside kicks, nor will it create any less onside kick collisions. With 4 on either side, now you don't know which way the kick is going, and R will have to spread out their players. That means fewer players to protect those that are catching the ball. And I can put the 4 to the off side of the kicker in motion toward the kick direction and have them at nearly full speed on a bouncing onside kick, while R is still going to have to keep 4 to the backside. This rule does nothing for safety.
And even the head of the Rules Committee fully admits that using the word kicker instead of ball was a big mistake. In his state, they have even changed the interp for less than four to each side of the kicker to be a foul AT THE TIME OF THE KICK, not at any time after the RFP. He has told officials, "Take a mental photo at the time of the kick", and that is the point where you decide if there is a foul. That's the NCAA rule, not what FED passed.
I have been told that the primary purpose of this rule was to eliminate the bunch kick. But this rule doesn't do that. The only way to do that is to require a certain amount of space between K players, or limit the number that may be between the hashes, or require a certain number outside each hash or the numbers.
I'm not questioning the motive of reducing injuries, but the application is misplaced.