That rule was put in place to increase competitiveness around the league. Imagine being a team with a ton of injuries going up against a fully stacked team of 53.
The rule I would change is Defensive Pass Interference. It needs to be tiered based on how far from the line of scrimmage it happened and how bad it was. Too many teams are getting freebie TDs on the 1 yard line. When you combine the low success rate of long passing plays with the possibility of PI getting called it makes taking those shots down the field more enticing than they should be.
If I can be greedy his Holiday season, the second rule I would change is the difference between a runner getting a TD and a receiver catching a TD in the end zone. These rules need to be more inline. It just doesn't make sense right now. Receivers are getting the shaft or maybe runners have it too easy.