Has there ever been a time where a rule change of this calibur was made mid season? I can not recall. This will be a huge deal down the road, and puts the players coaches, and refs in an awkward position. Soon we will see articles about how this drastically shifts the dynamic of the Pacers Heat series and the like. This could have waited until post season IMO.
Even though it was probably always intended to be a rule where you have to jump straight up in order to be considered vertical, the fact that they will be looking out specifically for this will cause issues.
The primary reason the series was competitive was because refs didn't blow the whistle when Hibbert contested shots.
The refs changed their minds in game 7 & you saw how quickly that game got out of hand.