Two questions on this...
Q1. Has a study been done comparing the rate of injury between the old style of onside kick and 4th and 15 plays ? ... I can't recall ever seeing a serious injury on an onside kick.
Q2. If under the proposed new rule you choose to kick off, how far does the ball have to travel before it isn't considered an onside kick ? 20 yards ? ...50 yards ? ...out of the end zone?
If they pass this rule I think they need to make defensive penalties on the 4th and 15 play reviewable.