I’ve been preaching this same thing for years. It would improve the game tenfold IMO. You get two challenges per game and everything is reviewable. If you get a challenge right or wrong, doesn’t matter, you still get only two challenges. In addition to this, replay has a “shot clock” of 2 minutes. If you can’t confirm or overturn after 2 minutes then it isn’t clear and obvious and the call on the field stands.
This is my fear. They will make it reviewable and then refuse to ever overturn it. Then it will mysteriously disappear after one year because it “didn’t work out”.