Banning hip drop tackles makes sense to people who don't know football. Yeah, those tackles can result in lower-body injuries. You know what causes more lower-body injuries? Playing on turf instead of natural grass. Hip drop tackles are tackles that happen when when a defender doesn't get the perfect angle to wrap up and throw his hips -- which happens all the freaking time.
On the other hand, the kickoff rule seems like it wasn't thought through at all.
What's the penalty for a late hit on the kicker, after a completed PAT or field goal? Fifteen yards assessed on the kickoff.
The thing is, with the new rule, nothing changes for the receiving team.
The kicker has the same, twenty yard window regardless. The other players don't move. Only the kicker moves fifteen yards forward. If anything, it makes it harder on the kicker, because every NFL kicker has a howitzer of a leg. It won't change the receiving team's field position at all.
So, basically, the NFL is relying on the good will of coaches and players to not just dive at the knees of kickers after the kick is off.
The new rule makes the roughing the kicker penalty a non-penalty.