I agree that practicality comes into it. IMO, if there's time enough for a replay to be squeezed in between two consecutive deliveries, there's time enough for those watching the review (ideally the third umpire, maybe the coach/team representative) to press a button indicating a decision to review. There could be reasonable restrictions - decide based on the one replay before the next delivery or forget it. There's no need to get the on-field players involved at all, IMO, unless it's for nicks where the batsman/fielder might be better suited to take a call on the spot.