If the NFL wants to increase the length of the season to 18 games and reduce the amount of injuries on special teams they should eliminate the kickoff (team gets the ball on the 20 yard line) and allow punt coverage team to go downfield as soon as the ball is snapped (instead of waiting until its punted).
Punt and kickoff coverage is where most of the injuries occur and the NFL would be wise to eliminate those plays. Then teams could carry more scrimmage players on their rosters instead of loading up on gunners and kick return specialists.
Thats another good reason to place the ball at the 20 yard line. Onside kicks are a waste of precious air time and are among the reason that NFL games more than 3 hours. If a team is hopelessly behind in the last 2 minutes there would be less reason to waste their timeouts and delay the telecast. It would actually be nice to see more game end in 3 hours or less so viewers wouldn't miss the start of the second game of the double-header.