The problem would that would be the players going mental and surrounding the referee, demanding he looked at the monitor every time something remotely contentious happened. You'd have to restrict each team to one appeal per half or something.
This is a great idea in theory. My worry is that the main money-spinning Premier League audiences in China etc won't agree. There does seem to be a split among people I know between anti VAR - people who go to games and pro VAR - people who only ever watch on TV.
30 second rule. The VAR has 30 seconds to decide whether to change the on field decision. If they can't make a call within 30 seconds then the on field decision stands.
It would mean clear and obvious errors get overturned, but really marginal ones don't. Then pay referees a lot more money and...