I think with technology you could get things like first downs/touchdowns, foot out of bounds, where the ball is spotted, etc worked out (some combination of GPS and sensors in the equipment) to the point you wouldn't need replay for those types of situations. Catch/Not a catch, fumbles, etc. might be more difficult. The issue nowadays is that the cameras are so much better than years ago that everything looks worse. Also back in the day you had less stuff to call because they didn't give a rip about player safety. I'm all for getting rid of anything that is subjective as long as it doesn't mean a guy getting his head ripped off.