I agree, but I wonder how often it would actually work right. Most of the time, if you can't tell very obviously that a ball crossed the goal line, it's because it's underneath a giant pile of bodies that would probably be blocking the view of that camera anyway.
What they need is some kind of chip technology that reads whether the ball crosses the line, but the weird shape of the ball probably makes that difficult too. You'd need a chip basically inserted into every outer most point on the oblong.