The danger comes when the referees start reviewing virtually everything because they're so afraid of being shown to be wrong. No cricket umpire makes an onfield decision about a run out any more, even if it's not close. Just in case. Rugby has got a bit that way too, and the constant stoppages have started to piss people off. But in both those cases the sports are much more stop/start anyway, especially cricket, so it doesn't matter so much. Four or five 1 minute delays for football is going to be pushing it, so finding a way to overcome human nature and make the referees use it sparingly is going to be the challenge - especially as one is bound to get it wrong.