I understand the CCA mechanics this year will be for the R to be even more involved in ball spotting than before. Also understand they are going to call for U to stay over the ball ANYTIME Team A subs, even if they sub as soon as the previous play ends.
The "logic" is that by having the R more involved in ball spotting, the ball can get made ready for play a bit faster than if we wait for the U to get it spotted. The U works outside to the sidelines if need be, relays the ball to the R, R puts it down and then goes back to his position.
But.....if the U then has to hustle in to get on the ball because A has subbed after the play, what have we gained? ? ? He might just as well hold on to the ball while coming in (thus preventing any snap) while A subs and B reacts.