You still have the problem of exactly where was the ball when the runners knee touched the ground. There are millions of scenarios. If the runner stretches his arms out when he is falling, the ball should be marked where the ball was when his knee touched the ground. If the runner is stopped but never really tackled (a bunch of guys have ahold of him and the ref stops the play), the ball is marked at the furthest point it was before he was stopped, and so on …
And a laser is not going to aid judging when the ball crosses the plane of the goal line. All it takes is one guy standing between the laser and the ball, and the laser will be rendered useless. So quickly, defensive coaches are going to assign guys to “screen” the laser.
Unless, of course, you used an x-ray laser and a lead football.
I’m all for that. 
Those are pretty difficult jobs to get. I believe that all NFL chain crew members are former college officials.
I’m not sure who colleges use, but it probably helps to know somebody in the athletics department.
The NFL uses two full sets of chains, one on each side, although one is “official” and that alternates sides during the game.
I think the NFL has two guys for the 10-yard chain, one guy for the down box, one guy to put down the orange line on the field to indicate the line, a guy to take care of the clip (which marks the big line that is used as a point of reference) and a guy who stands with the “start of drive” marker.
There is another crew like this on the other sideline.
In college ball, the sideline that doesn’t have the chains, usually just has a guy who puts down the first down marker and another guy with a down box.
I would try to be on a college chain crew. They stop the clock on first downs in college, so you don’t have to run as fast!