I don't think it would slow down the game too much at all. After all, how quickly do we see the incident on SKY after it happens, 5 seconds?
If an incident occurs in the area and a player goes down and the ball is booted out of play, then look at it right then.
If the above occurs but the ball stays in play for a while longer, then judge it when the ball next goes out of play. I wouldn't have a problem with that.
The only problem would be a team scoring a goal after a dubious decision, only to have the goal disallowed because it should have been a pen at the other end. Which I don't mind either.
Why don't I mind? Because fair is fair and right is right. It'snot the refs fault, it's the players fault for making the foul, onus back on the players and not on the refs or the fucking FA.
That FIFA have ignored video reffing for so long is a damning indictment of the corruption in the game. Rugby did it a while back and have never looked back, the game is a brilliant spectacle and fair as fuck, best team wins.